/*
   * Copyright (C) 2008, 2009 Intel Corporation
   * Authors: Andi Kleen, Fengguang Wu
   *
   * This software may be redistributed and/or modified under the terms of
   * the GNU General Public License ("GPL") version 2 only as published by the
   * Free Software Foundation.
   *
   * High level machine check handler. Handles pages reported by the

   * hardware as being corrupted usually due to a multi-bit ECC memory or cache

   * failure.

   * 
   * In addition there is a "soft offline" entry point that allows stop using
   * not-yet-corrupted-by-suspicious pages without killing anything.

   *
   * Handles page cache pages in various states.	The tricky part

   * here is that we can access any page asynchronously in respect to 
   * other VM users, because memory failures could happen anytime and 
   * anywhere. This could violate some of their assumptions. This is why 
   * this code has to be extremely careful. Generally it tries to use 
   * normal locking rules, as in get the standard locks, even if that means 
   * the error handling takes potentially a long time.
   * 
   * There are several operations here with exponential complexity because
   * of unsuitable VM data structures. For example the operation to map back 
   * from RMAP chains to processes has to walk the complete process list and 
   * has non linear complexity with the number. But since memory corruptions
   * are rare we hope to get away with this. This avoids impacting the core 
   * VM.

   */
  
  /*
   * Notebook:
   * - hugetlb needs more code
   * - kcore/oldmem/vmcore/mem/kmem check for hwpoison pages
   * - pass bad pages to kdump next kernel
   */

  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/page-flags.h>

  #include <linux/kernel-page-flags.h>

  #include <linux/sched.h>

  #include <linux/ksm.h>

  #include <linux/rmap.h>

  #include <linux/export.h>

  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <linux/backing-dev.h>

  #include <linux/migrate.h>
  #include <linux/page-isolation.h>
  #include <linux/suspend.h>

  #include <linux/slab.h>

  #include <linux/swapops.h>

  #include <linux/hugetlb.h>

  #include <linux/memory_hotplug.h>

  #include <linux/mm_inline.h>

  #include <linux/kfifo.h>

  #include "internal.h"
  
  int sysctl_memory_failure_early_kill __read_mostly = 0;
  
  int sysctl_memory_failure_recovery __read_mostly = 1;

  atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);

  #if defined(CONFIG_HWPOISON_INJECT) || defined(CONFIG_HWPOISON_INJECT_MODULE)

  u32 hwpoison_filter_enable = 0;

  u32 hwpoison_filter_dev_major = ~0U;
  u32 hwpoison_filter_dev_minor = ~0U;

  u64 hwpoison_filter_flags_mask;
  u64 hwpoison_filter_flags_value;

  EXPORT_SYMBOL_GPL(hwpoison_filter_enable);

  EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
  EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);

  EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
  EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);

  
  static int hwpoison_filter_dev(struct page *p)
  {
  	struct address_space *mapping;
  	dev_t dev;
  
  	if (hwpoison_filter_dev_major == ~0U &&
  	    hwpoison_filter_dev_minor == ~0U)
  		return 0;
  
  	/*

  	 * page_mapping() does not accept slab pages.

  	 */
  	if (PageSlab(p))
  		return -EINVAL;
  
  	mapping = page_mapping(p);
  	if (mapping == NULL || mapping->host == NULL)
  		return -EINVAL;
  
  	dev = mapping->host->i_sb->s_dev;
  	if (hwpoison_filter_dev_major != ~0U &&
  	    hwpoison_filter_dev_major != MAJOR(dev))
  		return -EINVAL;
  	if (hwpoison_filter_dev_minor != ~0U &&
  	    hwpoison_filter_dev_minor != MINOR(dev))
  		return -EINVAL;
  
  	return 0;
  }

  static int hwpoison_filter_flags(struct page *p)
  {
  	if (!hwpoison_filter_flags_mask)
  		return 0;
  
  	if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
  				    hwpoison_filter_flags_value)
  		return 0;
  	else
  		return -EINVAL;
  }

  /*
   * This allows stress tests to limit test scope to a collection of tasks
   * by putting them under some memcg. This prevents killing unrelated/important
   * processes such as /sbin/init. Note that the target task may share clean
   * pages with init (eg. libc text), which is harmless. If the target task
   * share _dirty_ pages with another task B, the test scheme must make sure B
   * is also included in the memcg. At last, due to race conditions this filter
   * can only guarantee that the page either belongs to the memcg tasks, or is
   * a freed page.
   */

  #ifdef	CONFIG_MEMCG_SWAP

  u64 hwpoison_filter_memcg;
  EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
  static int hwpoison_filter_task(struct page *p)
  {
  	struct mem_cgroup *mem;
  	struct cgroup_subsys_state *css;
  	unsigned long ino;
  
  	if (!hwpoison_filter_memcg)
  		return 0;
  
  	mem = try_get_mem_cgroup_from_page(p);
  	if (!mem)
  		return -EINVAL;
  
  	css = mem_cgroup_css(mem);
  	/* root_mem_cgroup has NULL dentries */
  	if (!css->cgroup->dentry)
  		return -EINVAL;
  
  	ino = css->cgroup->dentry->d_inode->i_ino;
  	css_put(css);
  
  	if (ino != hwpoison_filter_memcg)
  		return -EINVAL;
  
  	return 0;
  }
  #else
  static int hwpoison_filter_task(struct page *p) { return 0; }
  #endif

  int hwpoison_filter(struct page *p)
  {

  	if (!hwpoison_filter_enable)
  		return 0;

  	if (hwpoison_filter_dev(p))
  		return -EINVAL;

  	if (hwpoison_filter_flags(p))
  		return -EINVAL;

  	if (hwpoison_filter_task(p))
  		return -EINVAL;

  	return 0;
  }

  #else
  int hwpoison_filter(struct page *p)
  {
  	return 0;
  }
  #endif

  EXPORT_SYMBOL_GPL(hwpoison_filter);

  /*

   * Send all the processes who have the page mapped a signal.
   * ``action optional'' if they are not immediately affected by the error
   * ``action required'' if error happened in current execution context

   */

  static int kill_proc(struct task_struct *t, unsigned long addr, int trapno,
  			unsigned long pfn, struct page *page, int flags)

  {
  	struct siginfo si;
  	int ret;
  
  	printk(KERN_ERR

  		"MCE %#lx: Killing %s:%d due to hardware memory corruption
  ",

  		pfn, t->comm, t->pid);
  	si.si_signo = SIGBUS;
  	si.si_errno = 0;

  	si.si_addr = (void *)addr;
  #ifdef __ARCH_SI_TRAPNO
  	si.si_trapno = trapno;
  #endif

  	si.si_addr_lsb = compound_order(compound_head(page)) + PAGE_SHIFT;

  	if ((flags & MF_ACTION_REQUIRED) && t->mm == current->mm) {

  		si.si_code = BUS_MCEERR_AR;

  		ret = force_sig_info(SIGBUS, &si, current);

  	} else {
  		/*
  		 * Don't use force here, it's convenient if the signal
  		 * can be temporarily blocked.
  		 * This could cause a loop when the user sets SIGBUS
  		 * to SIG_IGN, but hopefully no one will do that?
  		 */
  		si.si_code = BUS_MCEERR_AO;
  		ret = send_sig_info(SIGBUS, &si, t);  /* synchronous? */
  	}

  	if (ret < 0)
  		printk(KERN_INFO "MCE: Error sending signal to %s:%d: %d
  ",
  		       t->comm, t->pid, ret);
  	return ret;
  }
  
  /*

   * When a unknown page type is encountered drain as many buffers as possible
   * in the hope to turn the page into a LRU or free page, which we can handle.
   */

  void shake_page(struct page *p, int access)

  {
  	if (!PageSlab(p)) {
  		lru_add_drain_all();
  		if (PageLRU(p))
  			return;
  		drain_all_pages();
  		if (PageLRU(p) || is_free_buddy_page(p))
  			return;
  	}

  	/*

  	 * Only call shrink_slab here (which would also shrink other caches) if
  	 * access is not potentially fatal.

  	 */

  	if (access) {
  		int nr;

  		int nid = page_to_nid(p);

  		do {

  			struct shrink_control shrink = {
  				.gfp_mask = GFP_KERNEL,

  			};

  			node_set(nid, shrink.nodes_to_scan);

  			nr = shrink_slab(&shrink, 1000, 1000);

  			if (page_count(p) == 1)

  				break;
  		} while (nr > 10);
  	}

  }
  EXPORT_SYMBOL_GPL(shake_page);
  
  /*

   * Kill all processes that have a poisoned page mapped and then isolate
   * the page.
   *
   * General strategy:
   * Find all processes having the page mapped and kill them.
   * But we keep a page reference around so that the page is not
   * actually freed yet.
   * Then stash the page away
   *
   * There's no convenient way to get back to mapped processes
   * from the VMAs. So do a brute-force search over all
   * running processes.
   *
   * Remember that machine checks are not common (or rather
   * if they are common you have other problems), so this shouldn't
   * be a performance issue.
   *
   * Also there are some races possible while we get from the
   * error detection to actually handle it.
   */
  
  struct to_kill {
  	struct list_head nd;
  	struct task_struct *tsk;
  	unsigned long addr;

  	char addr_valid;

  };
  
  /*
   * Failure handling: if we can't find or can't kill a process there's
   * not much we can do.	We just print a message and ignore otherwise.
   */
  
  /*
   * Schedule a process for later kill.
   * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
   * TBD would GFP_NOIO be enough?
   */
  static void add_to_kill(struct task_struct *tsk, struct page *p,
  		       struct vm_area_struct *vma,
  		       struct list_head *to_kill,
  		       struct to_kill **tkc)
  {
  	struct to_kill *tk;
  
  	if (*tkc) {
  		tk = *tkc;
  		*tkc = NULL;
  	} else {
  		tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
  		if (!tk) {
  			printk(KERN_ERR
  		"MCE: Out of memory while machine check handling
  ");
  			return;
  		}
  	}
  	tk->addr = page_address_in_vma(p, vma);
  	tk->addr_valid = 1;
  
  	/*
  	 * In theory we don't have to kill when the page was
  	 * munmaped. But it could be also a mremap. Since that's
  	 * likely very rare kill anyways just out of paranoia, but use
  	 * a SIGKILL because the error is not contained anymore.
  	 */
  	if (tk->addr == -EFAULT) {

  		pr_info("MCE: Unable to find user space address %lx in %s
  ",

  			page_to_pfn(p), tsk->comm);
  		tk->addr_valid = 0;
  	}
  	get_task_struct(tsk);
  	tk->tsk = tsk;
  	list_add_tail(&tk->nd, to_kill);
  }
  
  /*
   * Kill the processes that have been collected earlier.
   *
   * Only do anything when DOIT is set, otherwise just free the list
   * (this is used for clean pages which do not need killing)
   * Also when FAIL is set do a force kill because something went
   * wrong earlier.
   */

  static void kill_procs(struct list_head *to_kill, int forcekill, int trapno,

  			  int fail, struct page *page, unsigned long pfn,
  			  int flags)

  {
  	struct to_kill *tk, *next;
  
  	list_for_each_entry_safe (tk, next, to_kill, nd) {

  		if (forcekill) {

  			/*

  			 * In case something went wrong with munmapping

  			 * make sure the process doesn't catch the
  			 * signal and then access the memory. Just kill it.

  			 */
  			if (fail || tk->addr_valid == 0) {
  				printk(KERN_ERR
  		"MCE %#lx: forcibly killing %s:%d because of failure to unmap corrupted page
  ",
  					pfn, tk->tsk->comm, tk->tsk->pid);
  				force_sig(SIGKILL, tk->tsk);
  			}
  
  			/*
  			 * In theory the process could have mapped
  			 * something else on the address in-between. We could
  			 * check for that, but we need to tell the
  			 * process anyways.
  			 */

  			else if (kill_proc(tk->tsk, tk->addr, trapno,
  					      pfn, page, flags) < 0)

  				printk(KERN_ERR
  		"MCE %#lx: Cannot send advisory machine check signal to %s:%d
  ",
  					pfn, tk->tsk->comm, tk->tsk->pid);
  		}
  		put_task_struct(tk->tsk);
  		kfree(tk);
  	}
  }

  /*
   * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO)
   * on behalf of the thread group. Return task_struct of the (first found)
   * dedicated thread if found, and return NULL otherwise.
   *
   * We already hold read_lock(&tasklist_lock) in the caller, so we don't
   * have to call rcu_read_lock/unlock() in this function.
   */
  static struct task_struct *find_early_kill_thread(struct task_struct *tsk)

  {

  	struct task_struct *t;
  
  	for_each_thread(tsk, t)
  		if ((t->flags & PF_MCE_PROCESS) && (t->flags & PF_MCE_EARLY))
  			return t;
  	return NULL;
  }
  
  /*
   * Determine whether a given process is "early kill" process which expects
   * to be signaled when some page under the process is hwpoisoned.
   * Return task_struct of the dedicated thread (main thread unless explicitly
   * specified) if the process is "early kill," and otherwise returns NULL.
   */
  static struct task_struct *task_early_kill(struct task_struct *tsk,
  					   int force_early)
  {
  	struct task_struct *t;

  	if (!tsk->mm)

  		return NULL;

  	if (force_early)

  		return tsk;
  	t = find_early_kill_thread(tsk);
  	if (t)
  		return t;
  	if (sysctl_memory_failure_early_kill)
  		return tsk;
  	return NULL;

  }
  
  /*
   * Collect processes when the error hit an anonymous page.
   */
  static void collect_procs_anon(struct page *page, struct list_head *to_kill,

  			      struct to_kill **tkc, int force_early)

  {
  	struct vm_area_struct *vma;
  	struct task_struct *tsk;
  	struct anon_vma *av;

  	pgoff_t pgoff;

  	av = page_lock_anon_vma_read(page);

  	if (av == NULL)	/* Not actually mapped anymore */

  		return;

  	pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

  	read_lock(&tasklist_lock);

  	for_each_process (tsk) {

  		struct anon_vma_chain *vmac;

  		struct task_struct *t = task_early_kill(tsk, force_early);

  		if (!t)

  			continue;

  		anon_vma_interval_tree_foreach(vmac, &av->rb_root,
  					       pgoff, pgoff) {

  			vma = vmac->vma;

  			if (!page_mapped_in_vma(page, vma))
  				continue;

  			if (vma->vm_mm == t->mm)
  				add_to_kill(t, page, vma, to_kill, tkc);

  		}
  	}

  	read_unlock(&tasklist_lock);

  	page_unlock_anon_vma_read(av);

  }
  
  /*
   * Collect processes when the error hit a file mapped page.
   */
  static void collect_procs_file(struct page *page, struct list_head *to_kill,

  			      struct to_kill **tkc, int force_early)

  {
  	struct vm_area_struct *vma;
  	struct task_struct *tsk;

  	struct address_space *mapping = page->mapping;

  	mutex_lock(&mapping->i_mmap_mutex);

  	read_lock(&tasklist_lock);

  	for_each_process(tsk) {
  		pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

  		struct task_struct *t = task_early_kill(tsk, force_early);

  		if (!t)

  			continue;

  		vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,

  				      pgoff) {
  			/*
  			 * Send early kill signal to tasks where a vma covers
  			 * the page but the corrupted page is not necessarily
  			 * mapped it in its pte.
  			 * Assume applications who requested early kill want
  			 * to be informed of all such data corruptions.
  			 */

  			if (vma->vm_mm == t->mm)
  				add_to_kill(t, page, vma, to_kill, tkc);

  		}
  	}

  	read_unlock(&tasklist_lock);

  	mutex_unlock(&mapping->i_mmap_mutex);

  }
  
  /*
   * Collect the processes who have the corrupted page mapped to kill.
   * This is done in two steps for locking reasons.
   * First preallocate one tokill structure outside the spin locks,
   * so that we can kill at least one process reasonably reliable.
   */

  static void collect_procs(struct page *page, struct list_head *tokill,
  				int force_early)

  {
  	struct to_kill *tk;
  
  	if (!page->mapping)
  		return;
  
  	tk = kmalloc(sizeof(struct to_kill), GFP_NOIO);
  	if (!tk)
  		return;
  	if (PageAnon(page))

  		collect_procs_anon(page, tokill, &tk, force_early);

  	else

  		collect_procs_file(page, tokill, &tk, force_early);

  	kfree(tk);
  }
  
  /*
   * Error handlers for various types of pages.
   */
  
  enum outcome {

  	IGNORED,	/* Error: cannot be handled */
  	FAILED,		/* Error: handling failed */

  	DELAYED,	/* Will be handled later */

  	RECOVERED,	/* Successfully recovered */
  };
  
  static const char *action_name[] = {

  	[IGNORED] = "Ignored",

  	[FAILED] = "Failed",
  	[DELAYED] = "Delayed",

  	[RECOVERED] = "Recovered",
  };
  
  /*

   * XXX: It is possible that a page is isolated from LRU cache,
   * and then kept in swap cache or failed to remove from page cache.
   * The page count will stop it from being freed by unpoison.
   * Stress tests should be aware of this memory leak problem.
   */
  static int delete_from_lru_cache(struct page *p)
  {
  	if (!isolate_lru_page(p)) {
  		/*
  		 * Clear sensible page flags, so that the buddy system won't
  		 * complain when the page is unpoison-and-freed.
  		 */
  		ClearPageActive(p);
  		ClearPageUnevictable(p);
  		/*
  		 * drop the page count elevated by isolate_lru_page()
  		 */
  		page_cache_release(p);
  		return 0;
  	}
  	return -EIO;
  }
  
  /*

   * Error hit kernel page.
   * Do nothing, try to be lucky and not touch this instead. For a few cases we
   * could be more sophisticated.
   */
  static int me_kernel(struct page *p, unsigned long pfn)
  {

  	return IGNORED;
  }
  
  /*
   * Page in unknown state. Do nothing.
   */
  static int me_unknown(struct page *p, unsigned long pfn)
  {
  	printk(KERN_ERR "MCE %#lx: Unknown page state
  ", pfn);
  	return FAILED;
  }
  
  /*

   * Clean (or cleaned) page cache page.
   */
  static int me_pagecache_clean(struct page *p, unsigned long pfn)
  {
  	int err;
  	int ret = FAILED;
  	struct address_space *mapping;

  	delete_from_lru_cache(p);

  	/*
  	 * For anonymous pages we're done the only reference left
  	 * should be the one m_f() holds.
  	 */
  	if (PageAnon(p))
  		return RECOVERED;
  
  	/*
  	 * Now truncate the page in the page cache. This is really
  	 * more like a "temporary hole punch"
  	 * Don't do this for block devices when someone else
  	 * has a reference, because it could be file system metadata
  	 * and that's not safe to truncate.
  	 */
  	mapping = page_mapping(p);
  	if (!mapping) {
  		/*
  		 * Page has been teared down in the meanwhile
  		 */
  		return FAILED;
  	}
  
  	/*
  	 * Truncation is a bit tricky. Enable it per file system for now.
  	 *
  	 * Open: to take i_mutex or not for this? Right now we don't.
  	 */
  	if (mapping->a_ops->error_remove_page) {
  		err = mapping->a_ops->error_remove_page(mapping, p);
  		if (err != 0) {
  			printk(KERN_INFO "MCE %#lx: Failed to punch page: %d
  ",
  					pfn, err);
  		} else if (page_has_private(p) &&
  				!try_to_release_page(p, GFP_NOIO)) {

  			pr_info("MCE %#lx: failed to release buffers
  ", pfn);

  		} else {
  			ret = RECOVERED;
  		}
  	} else {
  		/*
  		 * If the file system doesn't support it just invalidate
  		 * This fails on dirty or anything with private pages
  		 */
  		if (invalidate_inode_page(p))
  			ret = RECOVERED;
  		else
  			printk(KERN_INFO "MCE %#lx: Failed to invalidate
  ",
  				pfn);
  	}
  	return ret;
  }
  
  /*
   * Dirty cache page page
   * Issues: when the error hit a hole page the error is not properly
   * propagated.
   */
  static int me_pagecache_dirty(struct page *p, unsigned long pfn)
  {
  	struct address_space *mapping = page_mapping(p);
  
  	SetPageError(p);
  	/* TBD: print more information about the file. */
  	if (mapping) {
  		/*
  		 * IO error will be reported by write(), fsync(), etc.
  		 * who check the mapping.
  		 * This way the application knows that something went
  		 * wrong with its dirty file data.
  		 *
  		 * There's one open issue:
  		 *
  		 * The EIO will be only reported on the next IO
  		 * operation and then cleared through the IO map.
  		 * Normally Linux has two mechanisms to pass IO error
  		 * first through the AS_EIO flag in the address space
  		 * and then through the PageError flag in the page.
  		 * Since we drop pages on memory failure handling the
  		 * only mechanism open to use is through AS_AIO.
  		 *
  		 * This has the disadvantage that it gets cleared on
  		 * the first operation that returns an error, while
  		 * the PageError bit is more sticky and only cleared
  		 * when the page is reread or dropped.  If an
  		 * application assumes it will always get error on
  		 * fsync, but does other operations on the fd before

  		 * and the page is dropped between then the error

  		 * will not be properly reported.
  		 *
  		 * This can already happen even without hwpoisoned
  		 * pages: first on metadata IO errors (which only
  		 * report through AS_EIO) or when the page is dropped
  		 * at the wrong time.
  		 *
  		 * So right now we assume that the application DTRT on
  		 * the first EIO, but we're not worse than other parts
  		 * of the kernel.
  		 */
  		mapping_set_error(mapping, EIO);
  	}
  
  	return me_pagecache_clean(p, pfn);
  }
  
  /*
   * Clean and dirty swap cache.
   *
   * Dirty swap cache page is tricky to handle. The page could live both in page
   * cache and swap cache(ie. page is freshly swapped in). So it could be
   * referenced concurrently by 2 types of PTEs:
   * normal PTEs and swap PTEs. We try to handle them consistently by calling
   * try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs,
   * and then
   *      - clear dirty bit to prevent IO
   *      - remove from LRU
   *      - but keep in the swap cache, so that when we return to it on
   *        a later page fault, we know the application is accessing
   *        corrupted data and shall be killed (we installed simple
   *        interception code in do_swap_page to catch it).
   *
   * Clean swap cache pages can be directly isolated. A later page fault will
   * bring in the known good data from disk.
   */
  static int me_swapcache_dirty(struct page *p, unsigned long pfn)
  {

  	ClearPageDirty(p);
  	/* Trigger EIO in shmem: */
  	ClearPageUptodate(p);

  	if (!delete_from_lru_cache(p))
  		return DELAYED;
  	else
  		return FAILED;

  }
  
  static int me_swapcache_clean(struct page *p, unsigned long pfn)
  {

  	delete_from_swap_cache(p);

  	if (!delete_from_lru_cache(p))
  		return RECOVERED;
  	else
  		return FAILED;

  }
  
  /*
   * Huge pages. Needs work.
   * Issues:

   * - Error on hugepage is contained in hugepage unit (not in raw page unit.)
   *   To narrow down kill region to one page, we need to break up pmd.

   */
  static int me_huge_page(struct page *p, unsigned long pfn)
  {

  	int res = 0;

  	struct page *hpage = compound_head(p);
  	/*
  	 * We can safely recover from error on free or reserved (i.e.
  	 * not in-use) hugepage by dequeuing it from freelist.
  	 * To check whether a hugepage is in-use or not, we can't use
  	 * page->lru because it can be used in other hugepage operations,
  	 * such as __unmap_hugepage_range() and gather_surplus_pages().
  	 * So instead we use page_mapping() and PageAnon().
  	 * We assume that this function is called with page lock held,
  	 * so there is no race between isolation and mapping/unmapping.
  	 */
  	if (!(page_mapping(hpage) || PageAnon(hpage))) {

  		res = dequeue_hwpoisoned_huge_page(hpage);
  		if (!res)
  			return RECOVERED;

  	}
  	return DELAYED;

  }
  
  /*
   * Various page states we can handle.
   *
   * A page state is defined by its current page->flags bits.
   * The table matches them in order and calls the right handler.
   *
   * This is quite tricky because we can access page at any time

   * in its live cycle, so all accesses have to be extremely careful.

   *
   * This is not complete. More states could be added.
   * For any missing state don't attempt recovery.
   */
  
  #define dirty		(1UL << PG_dirty)
  #define sc		(1UL << PG_swapcache)
  #define unevict		(1UL << PG_unevictable)
  #define mlock		(1UL << PG_mlocked)
  #define writeback	(1UL << PG_writeback)
  #define lru		(1UL << PG_lru)
  #define swapbacked	(1UL << PG_swapbacked)
  #define head		(1UL << PG_head)
  #define tail		(1UL << PG_tail)
  #define compound	(1UL << PG_compound)
  #define slab		(1UL << PG_slab)

  #define reserved	(1UL << PG_reserved)
  
  static struct page_state {
  	unsigned long mask;
  	unsigned long res;
  	char *msg;
  	int (*action)(struct page *p, unsigned long pfn);
  } error_states[] = {

  	{ reserved,	reserved,	"reserved kernel",	me_kernel },

  	/*
  	 * free pages are specially detected outside this table:
  	 * PG_buddy pages only make a small fraction of all free pages.
  	 */

  
  	/*
  	 * Could in theory check if slab page is free or if we can drop
  	 * currently unused objects without touching them. But just
  	 * treat it as standard kernel for now.
  	 */
  	{ slab,		slab,		"kernel slab",	me_kernel },
  
  #ifdef CONFIG_PAGEFLAGS_EXTENDED
  	{ head,		head,		"huge",		me_huge_page },
  	{ tail,		tail,		"huge",		me_huge_page },
  #else
  	{ compound,	compound,	"huge",		me_huge_page },
  #endif

  	{ sc|dirty,	sc|dirty,	"dirty swapcache",	me_swapcache_dirty },
  	{ sc|dirty,	sc,		"clean swapcache",	me_swapcache_clean },

  	{ mlock|dirty,	mlock|dirty,	"dirty mlocked LRU",	me_pagecache_dirty },

  	{ mlock|dirty,	mlock,		"clean mlocked LRU",	me_pagecache_clean },

  	{ unevict|dirty, unevict|dirty,	"dirty unevictable LRU", me_pagecache_dirty },

  	{ unevict|dirty, unevict,	"clean unevictable LRU", me_pagecache_clean },

  	{ lru|dirty,	lru|dirty,	"dirty LRU",	me_pagecache_dirty },

  	{ lru|dirty,	lru,		"clean LRU",	me_pagecache_clean },

  
  	/*
  	 * Catchall entry: must be at end.
  	 */
  	{ 0,		0,		"unknown page state",	me_unknown },
  };

  #undef dirty
  #undef sc
  #undef unevict
  #undef mlock
  #undef writeback
  #undef lru
  #undef swapbacked
  #undef head
  #undef tail
  #undef compound
  #undef slab
  #undef reserved

  /*
   * "Dirty/Clean" indication is not 100% accurate due to the possibility of
   * setting PG_dirty outside page lock. See also comment above set_page_dirty().
   */

  static void action_result(unsigned long pfn, char *msg, int result)
  {

  	pr_err("MCE %#lx: %s page recovery: %s
  ",
  		pfn, msg, action_name[result]);

  }
  
  static int page_action(struct page_state *ps, struct page *p,

  			unsigned long pfn)

  {
  	int result;

  	int count;

  
  	result = ps->action(p, pfn);
  	action_result(pfn, ps->msg, result);

  	count = page_count(p) - 1;

  	if (ps->action == me_swapcache_dirty && result == DELAYED)
  		count--;
  	if (count != 0) {

  		printk(KERN_ERR
  		       "MCE %#lx: %s page still referenced by %d users
  ",

  		       pfn, ps->msg, count);

  		result = FAILED;
  	}

  
  	/* Could do more checks here if page looks ok */
  	/*
  	 * Could adjust zone counters here to correct for the missing page.
  	 */

  	return (result == RECOVERED || result == DELAYED) ? 0 : -EBUSY;

  }

  /*
   * Do all that is necessary to remove user space mappings. Unmap
   * the pages and send SIGBUS to the processes if the data was dirty.
   */

  static int hwpoison_user_mappings(struct page *p, unsigned long pfn,

  				  int trapno, int flags, struct page **hpagep)

  {
  	enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
  	struct address_space *mapping;
  	LIST_HEAD(tokill);
  	int ret;

  	int kill = 1, forcekill;

  	struct page *hpage = *hpagep;

  	struct page *ppage;

  	if (PageReserved(p) || PageSlab(p))
  		return SWAP_SUCCESS;

  	/*
  	 * This check implies we don't kill processes if their pages
  	 * are in the swap cache early. Those are always late kills.
  	 */

  	if (!page_mapped(hpage))

  		return SWAP_SUCCESS;

  	if (PageKsm(p))

  		return SWAP_FAIL;

  
  	if (PageSwapCache(p)) {
  		printk(KERN_ERR
  		       "MCE %#lx: keeping poisoned page in swap cache
  ", pfn);
  		ttu |= TTU_IGNORE_HWPOISON;
  	}
  
  	/*
  	 * Propagate the dirty bit from PTEs to struct page first, because we
  	 * need this to decide if we should kill or just drop the page.

  	 * XXX: the dirty test could be racy: set_page_dirty() may not always
  	 * be called inside page lock (it's recommended but not enforced).

  	 */

  	mapping = page_mapping(hpage);

  	if (!(flags & MF_MUST_KILL) && !PageDirty(hpage) && mapping &&

  	    mapping_cap_writeback_dirty(mapping)) {
  		if (page_mkclean(hpage)) {
  			SetPageDirty(hpage);

  		} else {
  			kill = 0;
  			ttu |= TTU_IGNORE_HWPOISON;
  			printk(KERN_INFO
  	"MCE %#lx: corrupted page was clean: dropped without side effects
  ",
  				pfn);
  		}
  	}

  	/*
  	 * ppage: poisoned page
  	 *   if p is regular page(4k page)
  	 *        ppage == real poisoned page;
  	 *   else p is hugetlb or THP, ppage == head page.
  	 */
  	ppage = hpage;

  	if (PageTransHuge(hpage)) {
  		/*
  		 * Verify that this isn't a hugetlbfs head page, the check for
  		 * PageAnon is just for avoid tripping a split_huge_page
  		 * internal debug check, as split_huge_page refuses to deal with
  		 * anything that isn't an anon page. PageAnon can't go away fro
  		 * under us because we hold a refcount on the hpage, without a
  		 * refcount on the hpage. split_huge_page can't be safely called
  		 * in the first place, having a refcount on the tail isn't
  		 * enough * to be safe.
  		 */
  		if (!PageHuge(hpage) && PageAnon(hpage)) {
  			if (unlikely(split_huge_page(hpage))) {
  				/*
  				 * FIXME: if splitting THP is failed, it is
  				 * better to stop the following operation rather
  				 * than causing panic by unmapping. System might
  				 * survive if the page is freed later.
  				 */
  				printk(KERN_INFO
  					"MCE %#lx: failed to split THP
  ", pfn);
  
  				BUG_ON(!PageHWPoison(p));
  				return SWAP_FAIL;
  			}

  			/*
  			 * We pinned the head page for hwpoison handling,
  			 * now we split the thp and we are interested in
  			 * the hwpoisoned raw page, so move the refcount

  			 * to it. Similarly, page lock is shifted.

  			 */
  			if (hpage != p) {

  				if (!(flags & MF_COUNT_INCREASED)) {
  					put_page(hpage);
  					get_page(p);
  				}

  				lock_page(p);
  				unlock_page(hpage);
  				*hpagep = p;

  			}

  			/* THP is split, so ppage should be the real poisoned page. */
  			ppage = p;

  		}
  	}

  	/*
  	 * First collect all the processes that have the page
  	 * mapped in dirty form.  This has to be done before try_to_unmap,
  	 * because ttu takes the rmap data structures down.
  	 *
  	 * Error handling: We ignore errors here because
  	 * there's nothing that can be done.
  	 */
  	if (kill)

  		collect_procs(ppage, &tokill, flags & MF_ACTION_REQUIRED);

  	ret = try_to_unmap(ppage, ttu);

  	if (ret != SWAP_SUCCESS)
  		printk(KERN_ERR "MCE %#lx: failed to unmap page (mapcount=%d)
  ",

  				pfn, page_mapcount(ppage));

  	/*
  	 * Now that the dirty bit has been propagated to the
  	 * struct page and all unmaps done we can decide if
  	 * killing is needed or not.  Only kill when the page

  	 * was dirty or the process is not restartable,
  	 * otherwise the tokill list is merely

  	 * freed.  When there was a problem unmapping earlier
  	 * use a more force-full uncatchable kill to prevent
  	 * any accesses to the poisoned memory.
  	 */

  	forcekill = PageDirty(ppage) || (flags & MF_MUST_KILL);
  	kill_procs(&tokill, forcekill, trapno,

  		      ret != SWAP_SUCCESS, p, pfn, flags);

  
  	return ret;

  }

  static void set_page_hwpoison_huge_page(struct page *hpage)
  {
  	int i;

  	int nr_pages = 1 << compound_order(hpage);

  	for (i = 0; i < nr_pages; i++)
  		SetPageHWPoison(hpage + i);
  }
  
  static void clear_page_hwpoison_huge_page(struct page *hpage)
  {
  	int i;

  	int nr_pages = 1 << compound_order(hpage);

  	for (i = 0; i < nr_pages; i++)
  		ClearPageHWPoison(hpage + i);
  }

  /**
   * memory_failure - Handle memory failure of a page.
   * @pfn: Page Number of the corrupted page
   * @trapno: Trap number reported in the signal to user space.
   * @flags: fine tune action taken
   *
   * This function is called by the low level machine check code
   * of an architecture when it detects hardware memory corruption
   * of a page. It tries its best to recover, which includes
   * dropping pages, killing processes etc.
   *
   * The function is primarily of use for corruptions that
   * happen outside the current execution context (e.g. when
   * detected by a background scrubber)
   *
   * Must run in process context (e.g. a work queue) with interrupts
   * enabled and no spinlocks hold.
   */
  int memory_failure(unsigned long pfn, int trapno, int flags)

  {
  	struct page_state *ps;
  	struct page *p;

  	struct page *hpage;

  	int res;

  	unsigned int nr_pages;

  	unsigned long page_flags;

  
  	if (!sysctl_memory_failure_recovery)
  		panic("Memory failure from trap %d on page %lx", trapno, pfn);
  
  	if (!pfn_valid(pfn)) {

  		printk(KERN_ERR
  		       "MCE %#lx: memory outside kernel control
  ",
  		       pfn);
  		return -ENXIO;

  	}
  
  	p = pfn_to_page(pfn);

  	hpage = compound_head(p);

  	if (TestSetPageHWPoison(p)) {

  		printk(KERN_ERR "MCE %#lx: already hardware poisoned
  ", pfn);

  		return 0;
  	}

  	/*
  	 * Currently errors on hugetlbfs pages are measured in hugepage units,
  	 * so nr_pages should be 1 << compound_order.  OTOH when errors are on
  	 * transparent hugepages, they are supposed to be split and error
  	 * measurement is done in normal page units.  So nr_pages should be one
  	 * in this case.
  	 */
  	if (PageHuge(p))
  		nr_pages = 1 << compound_order(hpage);
  	else /* normal page or thp */
  		nr_pages = 1;

  	atomic_long_add(nr_pages, &num_poisoned_pages);

  
  	/*
  	 * We need/can do nothing about count=0 pages.
  	 * 1) it's a free page, and therefore in safe hand:
  	 *    prep_new_page() will be the gate keeper.

  	 * 2) it's a free hugepage, which is also safe:
  	 *    an affected hugepage will be dequeued from hugepage freelist,
  	 *    so there's no concern about reusing it ever after.
  	 * 3) it's part of a non-compound high order page.

  	 *    Implies some kernel user: cannot stop them from
  	 *    R/W the page; let's pray that the page has been
  	 *    used and will be freed some time later.
  	 * In fact it's dangerous to directly bump up page count from 0,
  	 * that may make page_freeze_refs()/page_unfreeze_refs() mismatch.
  	 */

  	if (!(flags & MF_COUNT_INCREASED) &&

  		!get_page_unless_zero(hpage)) {

  		if (is_free_buddy_page(p)) {
  			action_result(pfn, "free buddy", DELAYED);
  			return 0;

  		} else if (PageHuge(hpage)) {
  			/*

  			 * Check "filter hit" and "race with other subpage."

  			 */

  			lock_page(hpage);

  			if (PageHWPoison(hpage)) {
  				if ((hwpoison_filter(p) && TestClearPageHWPoison(p))
  				    || (p != hpage && TestSetPageHWPoison(hpage))) {
  					atomic_long_sub(nr_pages, &num_poisoned_pages);
  					unlock_page(hpage);
  					return 0;
  				}

  			}
  			set_page_hwpoison_huge_page(hpage);
  			res = dequeue_hwpoisoned_huge_page(hpage);
  			action_result(pfn, "free huge",
  				      res ? IGNORED : DELAYED);
  			unlock_page(hpage);
  			return res;

  		} else {
  			action_result(pfn, "high order kernel", IGNORED);
  			return -EBUSY;
  		}

  	}
  
  	/*

  	 * We ignore non-LRU pages for good reasons.
  	 * - PG_locked is only well defined for LRU pages and a few others
  	 * - to avoid races with __set_page_locked()
  	 * - to avoid races with __SetPageSlab*() (and more non-atomic ops)
  	 * The check (unnecessarily) ignores LRU pages being isolated and
  	 * walked by the page reclaim code, however that's not a big loss.
  	 */

  	if (!PageHuge(p) && !PageTransTail(p)) {

  		if (!PageLRU(p))
  			shake_page(p, 0);
  		if (!PageLRU(p)) {
  			/*
  			 * shake_page could have turned it free.
  			 */
  			if (is_free_buddy_page(p)) {

  				if (flags & MF_COUNT_INCREASED)
  					action_result(pfn, "free buddy", DELAYED);
  				else
  					action_result(pfn, "free buddy, 2nd try", DELAYED);

  				return 0;
  			}
  			action_result(pfn, "non LRU", IGNORED);
  			put_page(p);
  			return -EBUSY;

  		}

  	}

  
  	/*

  	 * Lock the page and wait for writeback to finish.
  	 * It's very difficult to mess with pages currently under IO
  	 * and in many cases impossible, so we just avoid it here.
  	 */

  	lock_page(hpage);

  
  	/*

  	 * We use page flags to determine what action should be taken, but
  	 * the flags can be modified by the error containment action.  One
  	 * example is an mlocked page, where PG_mlocked is cleared by
  	 * page_remove_rmap() in try_to_unmap_one(). So to determine page status
  	 * correctly, we save a copy of the page flags at this time.
  	 */
  	page_flags = p->flags;
  
  	/*

  	 * unpoison always clear PG_hwpoison inside page lock
  	 */
  	if (!PageHWPoison(p)) {

  		printk(KERN_ERR "MCE %#lx: just unpoisoned
  ", pfn);

  		atomic_long_sub(nr_pages, &num_poisoned_pages);
  		put_page(hpage);

  		res = 0;
  		goto out;
  	}

  	if (hwpoison_filter(p)) {
  		if (TestClearPageHWPoison(p))

  			atomic_long_sub(nr_pages, &num_poisoned_pages);

  		unlock_page(hpage);
  		put_page(hpage);

  		return 0;
  	}

  	/*
  	 * For error on the tail page, we should set PG_hwpoison
  	 * on the head page to show that the hugepage is hwpoisoned
  	 */

  	if (PageHuge(p) && PageTail(p) && TestSetPageHWPoison(hpage)) {

  		action_result(pfn, "hugepage already hardware poisoned",
  				IGNORED);
  		unlock_page(hpage);
  		put_page(hpage);
  		return 0;
  	}
  	/*
  	 * Set PG_hwpoison on all pages in an error hugepage,
  	 * because containment is done in hugepage unit for now.
  	 * Since we have done TestSetPageHWPoison() for the head page with
  	 * page lock held, we can safely set PG_hwpoison bits on tail pages.
  	 */
  	if (PageHuge(p))
  		set_page_hwpoison_huge_page(hpage);

  	wait_on_page_writeback(p);
  
  	/*
  	 * Now take care of user space mappings.

  	 * Abort on fail: __delete_from_page_cache() assumes unmapped page.

  	 *
  	 * When the raw error page is thp tail page, hpage points to the raw
  	 * page after thp split.

  	 */

  	if (hwpoison_user_mappings(p, pfn, trapno, flags, &hpage)
  	    != SWAP_SUCCESS) {

  		printk(KERN_ERR "MCE %#lx: cannot unmap page, give up
  ", pfn);
  		res = -EBUSY;
  		goto out;
  	}

  
  	/*
  	 * Torn down by someone else?
  	 */

  	if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) {

  		action_result(pfn, "already truncated LRU", IGNORED);

  		res = -EBUSY;

  		goto out;
  	}
  
  	res = -EBUSY;

  	/*
  	 * The first check uses the current page flags which may not have any
  	 * relevant information. The second check with the saved page flagss is
  	 * carried out only if the first check can't determine the page status.
  	 */
  	for (ps = error_states;; ps++)
  		if ((p->flags & ps->mask) == ps->res)

  			break;

  
  	page_flags |= (p->flags & (1UL << PG_dirty));

  	if (!ps->mask)
  		for (ps = error_states;; ps++)
  			if ((page_flags & ps->mask) == ps->res)
  				break;
  	res = page_action(ps, p, pfn);

  out:

  	unlock_page(hpage);

  	return res;
  }

  EXPORT_SYMBOL_GPL(memory_failure);

  #define MEMORY_FAILURE_FIFO_ORDER	4
  #define MEMORY_FAILURE_FIFO_SIZE	(1 << MEMORY_FAILURE_FIFO_ORDER)
  
  struct memory_failure_entry {
  	unsigned long pfn;
  	int trapno;
  	int flags;
  };
  
  struct memory_failure_cpu {
  	DECLARE_KFIFO(fifo, struct memory_failure_entry,
  		      MEMORY_FAILURE_FIFO_SIZE);
  	spinlock_t lock;
  	struct work_struct work;
  };
  
  static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);
  
  /**
   * memory_failure_queue - Schedule handling memory failure of a page.
   * @pfn: Page Number of the corrupted page
   * @trapno: Trap number reported in the signal to user space.
   * @flags: Flags for memory failure handling
   *
   * This function is called by the low level hardware error handler
   * when it detects hardware memory corruption of a page. It schedules
   * the recovering of error page, including dropping pages, killing
   * processes etc.
   *
   * The function is primarily of use for corruptions that
   * happen outside the current execution context (e.g. when
   * detected by a background scrubber)
   *
   * Can run in IRQ context.
   */
  void memory_failure_queue(unsigned long pfn, int trapno, int flags)
  {
  	struct memory_failure_cpu *mf_cpu;
  	unsigned long proc_flags;
  	struct memory_failure_entry entry = {
  		.pfn =		pfn,
  		.trapno =	trapno,
  		.flags =	flags,
  	};
  
  	mf_cpu = &get_cpu_var(memory_failure_cpu);
  	spin_lock_irqsave(&mf_cpu->lock, proc_flags);
  	if (kfifo_put(&mf_cpu->fifo, &entry))
  		schedule_work_on(smp_processor_id(), &mf_cpu->work);
  	else

  		pr_err("Memory failure: buffer overflow when queuing memory failure at %#lx
  ",

  		       pfn);
  	spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
  	put_cpu_var(memory_failure_cpu);
  }
  EXPORT_SYMBOL_GPL(memory_failure_queue);
  
  static void memory_failure_work_func(struct work_struct *work)
  {
  	struct memory_failure_cpu *mf_cpu;
  	struct memory_failure_entry entry = { 0, };
  	unsigned long proc_flags;
  	int gotten;
  
  	mf_cpu = &__get_cpu_var(memory_failure_cpu);
  	for (;;) {
  		spin_lock_irqsave(&mf_cpu->lock, proc_flags);
  		gotten = kfifo_get(&mf_cpu->fifo, &entry);
  		spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
  		if (!gotten)
  			break;

  		if (entry.flags & MF_SOFT_OFFLINE)
  			soft_offline_page(pfn_to_page(entry.pfn), entry.flags);
  		else
  			memory_failure(entry.pfn, entry.trapno, entry.flags);

  	}
  }
  
  static int __init memory_failure_init(void)
  {
  	struct memory_failure_cpu *mf_cpu;
  	int cpu;
  
  	for_each_possible_cpu(cpu) {
  		mf_cpu = &per_cpu(memory_failure_cpu, cpu);
  		spin_lock_init(&mf_cpu->lock);
  		INIT_KFIFO(mf_cpu->fifo);
  		INIT_WORK(&mf_cpu->work, memory_failure_work_func);
  	}
  
  	return 0;
  }
  core_initcall(memory_failure_init);

  /**
   * unpoison_memory - Unpoison a previously poisoned page
   * @pfn: Page number of the to be unpoisoned page
   *
   * Software-unpoison a page that has been poisoned by
   * memory_failure() earlier.
   *
   * This is only done on the software-level, so it only works
   * for linux injected failures, not real hardware failures
   *
   * Returns 0 for success, otherwise -errno.
   */
  int unpoison_memory(unsigned long pfn)
  {
  	struct page *page;
  	struct page *p;
  	int freeit = 0;

  	unsigned int nr_pages;

  
  	if (!pfn_valid(pfn))
  		return -ENXIO;
  
  	p = pfn_to_page(pfn);
  	page = compound_head(p);
  
  	if (!PageHWPoison(p)) {

  		pr_info("MCE: Page was already unpoisoned %#lx
  ", pfn);

  		return 0;
  	}

  	/*
  	 * unpoison_memory() can encounter thp only when the thp is being
  	 * worked by memory_failure() and the page lock is not held yet.
  	 * In such case, we yield to memory_failure() and make unpoison fail.
  	 */

  	if (!PageHuge(page) && PageTransHuge(page)) {

  		pr_info("MCE: Memory failure is now running on %#lx
  ", pfn);
  			return 0;
  	}

  	nr_pages = 1 << compound_order(page);

  	if (!get_page_unless_zero(page)) {

  		/*
  		 * Since HWPoisoned hugepage should have non-zero refcount,
  		 * race between memory failure and unpoison seems to happen.
  		 * In such case unpoison fails and memory failure runs
  		 * to the end.
  		 */
  		if (PageHuge(page)) {

  			pr_info("MCE: Memory failure is now running on free hugepage %#lx
  ", pfn);

  			return 0;
  		}

  		if (TestClearPageHWPoison(p))

  			atomic_long_dec(&num_poisoned_pages);

  		pr_info("MCE: Software-unpoisoned free page %#lx
  ", pfn);

  		return 0;
  	}

  	lock_page(page);

  	/*
  	 * This test is racy because PG_hwpoison is set outside of page lock.
  	 * That's acceptable because that won't trigger kernel panic. Instead,
  	 * the PG_hwpoison page will be caught and isolated on the entrance to
  	 * the free buddy page pool.
  	 */

  	if (TestClearPageHWPoison(page)) {

  		pr_info("MCE: Software-unpoisoned page %#lx
  ", pfn);

  		atomic_long_sub(nr_pages, &num_poisoned_pages);

  		freeit = 1;

  		if (PageHuge(page))
  			clear_page_hwpoison_huge_page(page);

  	}
  	unlock_page(page);
  
  	put_page(page);

  	if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))

  		put_page(page);
  
  	return 0;
  }
  EXPORT_SYMBOL(unpoison_memory);

  
  static struct page *new_page(struct page *p, unsigned long private, int **x)
  {

  	int nid = page_to_nid(p);

  	if (PageHuge(p))
  		return alloc_huge_page_node(page_hstate(compound_head(p)),
  						   nid);
  	else
  		return alloc_pages_exact_node(nid, GFP_HIGHUSER_MOVABLE, 0);

  }
  
  /*
   * Safely get reference count of an arbitrary page.
   * Returns 0 for a free page, -EIO for a zero refcount page
   * that is not free, and 1 for any other page type.
   * For 1 the page is returned with increased page count, otherwise not.
   */

  static int __get_any_page(struct page *p, unsigned long pfn, int flags)

  {
  	int ret;
  
  	if (flags & MF_COUNT_INCREASED)
  		return 1;
  
  	/*

  	 * The lock_memory_hotplug prevents a race with memory hotplug.

  	 * This is a big hammer, a better would be nicer.
  	 */

  	lock_memory_hotplug();

  
  	/*
  	 * Isolate the page, so that it doesn't get reallocated if it

  	 * was free. This flag should be kept set until the source page
  	 * is freed and PG_hwpoison on it is set.

  	 */

  	if (get_pageblock_migratetype(p) != MIGRATE_ISOLATE)
  		set_migratetype_isolate(p, true);

  	/*
  	 * When the target page is a free hugepage, just remove it
  	 * from free hugepage list.
  	 */

  	if (!get_page_unless_zero(compound_head(p))) {

  		if (PageHuge(p)) {

  			pr_info("%s: %#lx free huge page
  ", __func__, pfn);

  			ret = 0;

  		} else if (is_free_buddy_page(p)) {

  			pr_info("%s: %#lx free buddy page
  ", __func__, pfn);

  			ret = 0;
  		} else {

  			pr_info("%s: %#lx: unknown zero refcount page type %lx
  ",
  				__func__, pfn, p->flags);

  			ret = -EIO;
  		}
  	} else {
  		/* Not a free page */
  		ret = 1;
  	}

  	unlock_memory_hotplug();

  	return ret;
  }

  static int get_any_page(struct page *page, unsigned long pfn, int flags)
  {
  	int ret = __get_any_page(page, pfn, flags);
  
  	if (ret == 1 && !PageHuge(page) && !PageLRU(page)) {
  		/*
  		 * Try to free it.
  		 */
  		put_page(page);
  		shake_page(page, 1);
  
  		/*
  		 * Did it turn free?
  		 */
  		ret = __get_any_page(page, pfn, 0);
  		if (!PageLRU(page)) {
  			pr_info("soft_offline: %#lx: unknown non LRU page type %lx
  ",
  				pfn, page->flags);
  			return -EIO;
  		}
  	}
  	return ret;
  }

  static int soft_offline_huge_page(struct page *page, int flags)
  {
  	int ret;
  	unsigned long pfn = page_to_pfn(page);
  	struct page *hpage = compound_head(page);

  	LIST_HEAD(pagelist);

  	/*
  	 * This double-check of PageHWPoison is to avoid the race with
  	 * memory_failure(). See also comment in __soft_offline_page().
  	 */
  	lock_page(hpage);

  	if (PageHWPoison(hpage)) {

  		unlock_page(hpage);
  		put_page(hpage);

  		pr_info("soft offline: %#lx hugepage already poisoned
  ", pfn);

  		return -EBUSY;

  	}

  	unlock_page(hpage);

  	/* Keep page count to indicate a given hugepage is isolated. */

  	list_move(&hpage->lru, &pagelist);

  	ret = migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL,

  				MIGRATE_SYNC, MR_MEMORY_FAILURE);

  	if (ret) {

  		pr_info("soft offline: %#lx: migration failed %d, type %lx
  ",
  			pfn, ret, page->flags);

  		/*
  		 * We know that soft_offline_huge_page() tries to migrate
  		 * only one hugepage pointed to by hpage, so we need not
  		 * run through the pagelist here.
  		 */
  		putback_active_hugepage(hpage);
  		if (ret > 0)
  			ret = -EIO;

  	} else {

  		/* overcommit hugetlb page will be freed to buddy */
  		if (PageHuge(page)) {
  			set_page_hwpoison_huge_page(hpage);
  			dequeue_hwpoisoned_huge_page(hpage);
  			atomic_long_add(1 << compound_order(hpage),
  					&num_poisoned_pages);
  		} else {
  			SetPageHWPoison(page);
  			atomic_long_inc(&num_poisoned_pages);
  		}

  	}

  	return ret;
  }

  static int __soft_offline_page(struct page *page, int flags)
  {
  	int ret;
  	unsigned long pfn = page_to_pfn(page);

  	/*

  	 * Check PageHWPoison again inside page lock because PageHWPoison
  	 * is set by memory_failure() outside page lock. Note that
  	 * memory_failure() also double-checks PageHWPoison inside page lock,
  	 * so there's no race between soft_offline_page() and memory_failure().

  	 */

  	lock_page(page);
  	wait_on_page_writeback(page);

  	if (PageHWPoison(page)) {
  		unlock_page(page);
  		put_page(page);
  		pr_info("soft offline: %#lx page already poisoned
  ", pfn);
  		return -EBUSY;
  	}

  	/*
  	 * Try to invalidate first. This should work for
  	 * non dirty unmapped page cache pages.
  	 */
  	ret = invalidate_inode_page(page);
  	unlock_page(page);

  	/*

  	 * RED-PEN would be better to keep it isolated here, but we
  	 * would need to fix isolation locking first.
  	 */

  	if (ret == 1) {

  		put_page(page);

  		pr_info("soft_offline: %#lx: invalidated
  ", pfn);

  		SetPageHWPoison(page);
  		atomic_long_inc(&num_poisoned_pages);
  		return 0;

  	}
  
  	/*
  	 * Simple invalidation didn't work.
  	 * Try to migrate to a new page instead. migrate.c
  	 * handles a large number of cases for us.
  	 */
  	ret = isolate_lru_page(page);

  	/*
  	 * Drop page reference which is came from get_any_page()
  	 * successful isolate_lru_page() already took another one.
  	 */
  	put_page(page);

  	if (!ret) {
  		LIST_HEAD(pagelist);

  		inc_zone_page_state(page, NR_ISOLATED_ANON +

  					page_is_file_cache(page));

  		list_add(&page->lru, &pagelist);

  		ret = migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL,

  					MIGRATE_SYNC, MR_MEMORY_FAILURE);

  		if (ret) {

  			putback_lru_pages(&pagelist);

  			pr_info("soft offline: %#lx: migration failed %d, type %lx
  ",

  				pfn, ret, page->flags);
  			if (ret > 0)
  				ret = -EIO;

  		} else {

  			/*
  			 * After page migration succeeds, the source page can
  			 * be trapped in pagevec and actual freeing is delayed.
  			 * Freeing code works differently based on PG_hwpoison,
  			 * so there's a race. We need to make sure that the
  			 * source page should be freed back to buddy before
  			 * setting PG_hwpoison.
  			 */
  			if (!is_free_buddy_page(page))
  				lru_add_drain_all();
  			if (!is_free_buddy_page(page))
  				drain_all_pages();

  			SetPageHWPoison(page);

  			if (!is_free_buddy_page(page))
  				pr_info("soft offline: %#lx: page leaked
  ",
  					pfn);

  			atomic_long_inc(&num_poisoned_pages);

  		}
  	} else {

  		pr_info("soft offline: %#lx: isolation failed: %d, page count %d, type %lx
  ",

  			pfn, ret, page_count(page), page->flags);

  	}

  	return ret;
  }

  
  /**
   * soft_offline_page - Soft offline a page.
   * @page: page to offline
   * @flags: flags. Same as memory_failure().
   *
   * Returns 0 on success, otherwise negated errno.
   *
   * Soft offline a page, by migration or invalidation,
   * without killing anything. This is for the case when
   * a page is not corrupted yet (so it's still valid to access),
   * but has had a number of corrected errors and is better taken
   * out.
   *
   * The actual policy on when to do that is maintained by
   * user space.
   *
   * This should never impact any application or cause data loss,
   * however it might take some time.
   *
   * This is not a 100% solution for all memory, but tries to be
   * ``good enough'' for the majority of memory.
   */
  int soft_offline_page(struct page *page, int flags)
  {
  	int ret;
  	unsigned long pfn = page_to_pfn(page);

  	struct page *hpage = compound_head(page);

  
  	if (PageHWPoison(page)) {
  		pr_info("soft offline: %#lx page already poisoned
  ", pfn);
  		return -EBUSY;
  	}
  	if (!PageHuge(page) && PageTransHuge(hpage)) {
  		if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
  			pr_info("soft offline: %#lx: failed to split THP
  ",
  				pfn);
  			return -EBUSY;
  		}
  	}
  
  	ret = get_any_page(page, pfn, flags);
  	if (ret < 0)
  		goto unset;
  	if (ret) { /* for in-use pages */
  		if (PageHuge(page))
  			ret = soft_offline_huge_page(page, flags);
  		else
  			ret = __soft_offline_page(page, flags);
  	} else { /* for free pages */
  		if (PageHuge(page)) {
  			set_page_hwpoison_huge_page(hpage);
  			dequeue_hwpoisoned_huge_page(hpage);
  			atomic_long_add(1 << compound_order(hpage),
  					&num_poisoned_pages);
  		} else {
  			SetPageHWPoison(page);
  			atomic_long_inc(&num_poisoned_pages);
  		}
  	}
  unset:
  	unset_migratetype_isolate(page, MIGRATE_MOVABLE);
  	return ret;
  }