/*
   *  linux/mm/oom_kill.c
   * 
   *  Copyright (C)  1998,2000  Rik van Riel
   *	Thanks go out to Claus Fischer for some serious inspiration and
   *	for goading me into coding this file...

   *  Copyright (C)  2010  Google, Inc.
   *	Rewritten by David Rientjes

   *
   *  The routines in this file are used to kill a process when

   *  we're seriously out of memory. This gets called from __alloc_pages()
   *  in mm/page_alloc.c when we really run out of memory.

   *
   *  Since we won't call these routines often (on a well-configured
   *  machine) this file will double as a 'coding guide' and a signpost
   *  for newbie kernel hackers. It features several pointers to major
   *  kernel subsystems and hints as to where to find out what things do.
   */

  #include <linux/oom.h>

  #include <linux/mm.h>

  #include <linux/err.h>

  #include <linux/gfp.h>

  #include <linux/sched.h>
  #include <linux/swap.h>
  #include <linux/timex.h>
  #include <linux/jiffies.h>

  #include <linux/cpuset.h>

  #include <linux/export.h>

  #include <linux/notifier.h>

  #include <linux/memcontrol.h>

  #include <linux/mempolicy.h>

  #include <linux/security.h>

  #include <linux/ptrace.h>

  #include <linux/freezer.h>

  #include <linux/ftrace.h>
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/oom.h>

  int sysctl_panic_on_oom;

  int sysctl_oom_kill_allocating_task;

  int sysctl_oom_dump_tasks = 1;

  static DEFINE_SPINLOCK(zone_scan_lock);

  /*
   * compare_swap_oom_score_adj() - compare and swap current's oom_score_adj
   * @old_val: old oom_score_adj for compare
   * @new_val: new oom_score_adj for swap
   *
   * Sets the oom_score_adj value for current to @new_val iff its present value is
   * @old_val.  Usually used to reinstate a previous value to prevent racing with
   * userspacing tuning the value in the interim.
   */
  void compare_swap_oom_score_adj(int old_val, int new_val)
  {
  	struct sighand_struct *sighand = current->sighand;
  
  	spin_lock_irq(&sighand->siglock);
  	if (current->signal->oom_score_adj == old_val)
  		current->signal->oom_score_adj = new_val;

  	trace_oom_score_adj_update(current);

  	spin_unlock_irq(&sighand->siglock);
  }

  /**
   * test_set_oom_score_adj() - set current's oom_score_adj and return old value
   * @new_val: new oom_score_adj value
   *
   * Sets the oom_score_adj value for current to @new_val with proper
   * synchronization and returns the old value.  Usually used to temporarily
   * set a value, save the old value in the caller, and then reinstate it later.
   */
  int test_set_oom_score_adj(int new_val)
  {
  	struct sighand_struct *sighand = current->sighand;
  	int old_val;
  
  	spin_lock_irq(&sighand->siglock);
  	old_val = current->signal->oom_score_adj;

  	current->signal->oom_score_adj = new_val;

  	trace_oom_score_adj_update(current);

  	spin_unlock_irq(&sighand->siglock);
  
  	return old_val;
  }

  #ifdef CONFIG_NUMA
  /**
   * has_intersects_mems_allowed() - check task eligiblity for kill
   * @tsk: task struct of which task to consider
   * @mask: nodemask passed to page allocator for mempolicy ooms
   *
   * Task eligibility is determined by whether or not a candidate task, @tsk,
   * shares the same mempolicy nodes as current if it is bound by such a policy
   * and whether or not it has the same set of allowed cpuset nodes.

   */

  static bool has_intersects_mems_allowed(struct task_struct *tsk,
  					const nodemask_t *mask)

  {

  	struct task_struct *start = tsk;

  	do {

  		if (mask) {
  			/*
  			 * If this is a mempolicy constrained oom, tsk's
  			 * cpuset is irrelevant.  Only return true if its
  			 * mempolicy intersects current, otherwise it may be
  			 * needlessly killed.
  			 */
  			if (mempolicy_nodemask_intersects(tsk, mask))
  				return true;
  		} else {
  			/*
  			 * This is not a mempolicy constrained oom, so only
  			 * check the mems of tsk's cpuset.
  			 */
  			if (cpuset_mems_allowed_intersects(current, tsk))
  				return true;
  		}

  	} while_each_thread(start, tsk);

  	return false;
  }
  #else
  static bool has_intersects_mems_allowed(struct task_struct *tsk,
  					const nodemask_t *mask)
  {
  	return true;

  }

  #endif /* CONFIG_NUMA */

  /*
   * The process p may have detached its own ->mm while exiting or through
   * use_mm(), but one or more of its subthreads may still have a valid
   * pointer.  Return p, or any of its subthreads with a valid ->mm, with
   * task_lock() held.
   */

  struct task_struct *find_lock_task_mm(struct task_struct *p)

  {
  	struct task_struct *t = p;
  
  	do {
  		task_lock(t);
  		if (likely(t->mm))
  			return t;
  		task_unlock(t);
  	} while_each_thread(p, t);
  
  	return NULL;
  }

  /* return true if the task is not adequate as candidate victim task. */

  static bool oom_unkillable_task(struct task_struct *p,

  		const struct mem_cgroup *memcg, const nodemask_t *nodemask)

  {
  	if (is_global_init(p))
  		return true;
  	if (p->flags & PF_KTHREAD)
  		return true;
  
  	/* When mem_cgroup_out_of_memory() and p is not member of the group */

  	if (memcg && !task_in_mem_cgroup(p, memcg))

  		return true;
  
  	/* p may not have freeable memory in nodemask */
  	if (!has_intersects_mems_allowed(p, nodemask))
  		return true;
  
  	return false;
  }

  /**

   * oom_badness - heuristic function to determine which candidate task to kill

   * @p: task struct of which task we should calculate

   * @totalpages: total present RAM allowed for page allocation

   *

   * The heuristic for determining which task to kill is made to be as simple and
   * predictable as possible.  The goal is to return the highest value for the
   * task consuming the most memory to avoid subsequent oom failures.

   */

  unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *memcg,

  		      const nodemask_t *nodemask, unsigned long totalpages)

  {

  	long points;

  	if (oom_unkillable_task(p, memcg, nodemask))

  		return 0;

  	p = find_lock_task_mm(p);
  	if (!p)

  		return 0;

  	if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
  		task_unlock(p);
  		return 0;
  	}

  	/*

  	 * The memory controller may have a limit of 0 bytes, so avoid a divide
  	 * by zero, if necessary.

  	 */

  	if (!totalpages)
  		totalpages = 1;

  
  	/*

  	 * The baseline for the badness score is the proportion of RAM that each

  	 * task's rss, pagetable and swap space use.

  	 */

  	points = get_mm_rss(p->mm) + p->mm->nr_ptes;
  	points += get_mm_counter(p->mm, MM_SWAPENTS);
  
  	points *= 1000;
  	points /= totalpages;

  	task_unlock(p);

  
  	/*

  	 * Root processes get 3% bonus, just like the __vm_enough_memory()
  	 * implementation used by LSMs.

  	 */

  	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
  		points -= 30;

  
  	/*

  	 * /proc/pid/oom_score_adj ranges from -1000 to +1000 such that it may
  	 * either completely disable oom killing or always prefer a certain
  	 * task.

  	 */

  	points += p->signal->oom_score_adj;

  	/*
  	 * Never return 0 for an eligible task that may be killed since it's
  	 * possible that no single user task uses more than 0.1% of memory and
  	 * no single admin tasks uses more than 3.0%.
  	 */
  	if (points <= 0)
  		return 1;

  	return (points < 1000) ? points : 1000;

  }
  
  /*

   * Determine the type of allocation constraint.
   */

  #ifdef CONFIG_NUMA

  static enum oom_constraint constrained_alloc(struct zonelist *zonelist,

  				gfp_t gfp_mask, nodemask_t *nodemask,
  				unsigned long *totalpages)

  {

  	struct zone *zone;

  	struct zoneref *z;

  	enum zone_type high_zoneidx = gfp_zone(gfp_mask);

  	bool cpuset_limited = false;
  	int nid;

  	/* Default to all available memory */
  	*totalpages = totalram_pages + total_swap_pages;
  
  	if (!zonelist)
  		return CONSTRAINT_NONE;

  	/*
  	 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
  	 * to kill current.We have to random task kill in this case.
  	 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
  	 */
  	if (gfp_mask & __GFP_THISNODE)
  		return CONSTRAINT_NONE;

  	/*

  	 * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
  	 * the page allocator means a mempolicy is in effect.  Cpuset policy
  	 * is enforced in get_page_from_freelist().

  	 */

  	if (nodemask && !nodes_subset(node_states[N_HIGH_MEMORY], *nodemask)) {
  		*totalpages = total_swap_pages;
  		for_each_node_mask(nid, *nodemask)
  			*totalpages += node_spanned_pages(nid);

  		return CONSTRAINT_MEMORY_POLICY;

  	}

  
  	/* Check this allocation failure is caused by cpuset's wall function */
  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
  			high_zoneidx, nodemask)
  		if (!cpuset_zone_allowed_softwall(zone, gfp_mask))

  			cpuset_limited = true;

  	if (cpuset_limited) {
  		*totalpages = total_swap_pages;
  		for_each_node_mask(nid, cpuset_current_mems_allowed)
  			*totalpages += node_spanned_pages(nid);
  		return CONSTRAINT_CPUSET;
  	}

  	return CONSTRAINT_NONE;
  }

  #else
  static enum oom_constraint constrained_alloc(struct zonelist *zonelist,

  				gfp_t gfp_mask, nodemask_t *nodemask,
  				unsigned long *totalpages)

  {

  	*totalpages = totalram_pages + total_swap_pages;

  	return CONSTRAINT_NONE;
  }
  #endif

  
  /*

   * Simple selection loop. We chose the process with the highest
   * number of 'points'. We expect the caller will lock the tasklist.
   *
   * (not docbooked, we don't want this one cluttering up the manual)
   */

  static struct task_struct *select_bad_process(unsigned int *ppoints,

  		unsigned long totalpages, struct mem_cgroup *memcg,

  		const nodemask_t *nodemask)

  {

  	struct task_struct *g, *p;

  	struct task_struct *chosen = NULL;

  	*ppoints = 0;

  	do_each_thread(g, p) {

  		unsigned int points;

  		if (p->exit_state)

  			continue;

  		if (oom_unkillable_task(p, memcg, nodemask))

  			continue;

  		/*

  		 * This task already has access to memory reserves and is
  		 * being killed. Don't allow any other task access to the
  		 * memory reserve.
  		 *
  		 * Note: this may have a chance of deadlock if it gets
  		 * blocked waiting for another task which itself is waiting
  		 * for memory. Is there a better alternative?
  		 */

  		if (test_tsk_thread_flag(p, TIF_MEMDIE)) {
  			if (unlikely(frozen(p)))

  				__thaw_task(p);

  			return ERR_PTR(-1UL);

  		}

  		if (!p->mm)
  			continue;

  		if (p->flags & PF_EXITING) {

  			/*
  			 * If p is the current task and is in the process of
  			 * releasing memory, we allow the "kill" to set
  			 * TIF_MEMDIE, which will allow it to gain access to
  			 * memory reserves.  Otherwise, it may stall forever.
  			 *
  			 * The loop isn't broken here, however, in case other
  			 * threads are found to have already been oom killed.
  			 */
  			if (p == current) {
  				chosen = p;
  				*ppoints = 1000;
  			} else {
  				/*
  				 * If this task is not being ptraced on exit,
  				 * then wait for it to finish before killing
  				 * some other task unnecessarily.
  				 */

  				if (!(p->group_leader->ptrace & PT_TRACE_EXIT))

  					return ERR_PTR(-1UL);
  			}

  		}

  		points = oom_badness(p, memcg, nodemask, totalpages);

  		if (points > *ppoints) {

  			chosen = p;

  			*ppoints = points;

  		}

  	} while_each_thread(g, p);

  	return chosen;
  }
  
  /**

   * dump_tasks - dump current memory state of all system tasks

   * @mem: current's memory controller, if constrained

   * @nodemask: nodemask passed to page allocator for mempolicy ooms

   *

   * Dumps the current memory state of all eligible tasks.  Tasks not in the same
   * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
   * are not shown.

   * State information includes task's pid, uid, tgid, vm size, rss, cpu, oom_adj

   * value, oom_score_adj value, and name.

   *

   * Call with tasklist_lock read-locked.
   */

  static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemask)

  {

  	struct task_struct *p;
  	struct task_struct *task;

  	pr_info("[ pid ]   uid  tgid total_vm      rss cpu oom_adj oom_score_adj name
  ");

  	for_each_process(p) {

  		if (oom_unkillable_task(p, memcg, nodemask))

  			continue;

  		task = find_lock_task_mm(p);
  		if (!task) {

  			/*

  			 * This is a kthread or all of p's threads have already
  			 * detached their mm's.  There's no need to report

  			 * them; they can't be oom killed anyway.

  			 */

  			continue;
  		}

  		pr_info("[%5d] %5d %5d %8lu %8lu %3u     %3d         %5d %s
  ",

  			task->pid, task_uid(task), task->tgid,

  			task->mm->total_vm, get_mm_rss(task->mm),
  			task_cpu(task), task->signal->oom_adj,
  			task->signal->oom_score_adj, task->comm);

  		task_unlock(task);
  	}

  }

  static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,

  			struct mem_cgroup *memcg, const nodemask_t *nodemask)

  {

  	task_lock(current);

  	pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, "

  		"oom_adj=%d, oom_score_adj=%d
  ",
  		current->comm, gfp_mask, order, current->signal->oom_adj,
  		current->signal->oom_score_adj);

  	cpuset_print_task_mems_allowed(current);
  	task_unlock(current);
  	dump_stack();

  	mem_cgroup_print_oom_info(memcg, p);

  	show_mem(SHOW_MEM_FILTER_NODES);

  	if (sysctl_oom_dump_tasks)

  		dump_tasks(memcg, nodemask);

  }

  #define K(x) ((x) << (PAGE_SHIFT-10))

  static int oom_kill_task(struct task_struct *p)

  {

  	struct task_struct *q;
  	struct mm_struct *mm;

  	p = find_lock_task_mm(p);

  	if (!p)

  		return 1;

  	/* mm cannot be safely dereferenced after task_unlock(p) */
  	mm = p->mm;

  	pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB
  ",
  		task_pid_nr(p), p->comm, K(p->mm->total_vm),
  		K(get_mm_counter(p->mm, MM_ANONPAGES)),
  		K(get_mm_counter(p->mm, MM_FILEPAGES)));

  	task_unlock(p);

  	/*

  	 * Kill all user processes sharing p->mm in other thread groups, if any.

  	 * They don't get access to memory reserves or a higher scheduler
  	 * priority, though, to avoid depletion of all memory or task
  	 * starvation.  This prevents mm->mmap_sem livelock when an oom killed
  	 * task cannot exit because it requires the semaphore and its contended
  	 * by another thread trying to allocate memory itself.  That thread will
  	 * now get access to memory reserves since it has a pending fatal
  	 * signal.
  	 */
  	for_each_process(q)

  		if (q->mm == mm && !same_thread_group(q, p) &&
  		    !(q->flags & PF_KTHREAD)) {

  			if (q->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
  				continue;

  			task_lock(q);	/* Protect ->comm from prctl() */
  			pr_err("Kill process %d (%s) sharing same memory
  ",
  				task_pid_nr(q), q->comm);
  			task_unlock(q);
  			force_sig(SIGKILL, q);
  		}

  	set_tsk_thread_flag(p, TIF_MEMDIE);

  	force_sig(SIGKILL, p);

  	return 0;

  }

  #undef K

  static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,

  			    unsigned int points, unsigned long totalpages,

  			    struct mem_cgroup *memcg, nodemask_t *nodemask,

  			    const char *message)

  {

  	struct task_struct *victim = p;

  	struct task_struct *child;

  	struct task_struct *t = p;
  	unsigned int victim_points = 0;

  	if (printk_ratelimit())

  		dump_header(p, gfp_mask, order, memcg, nodemask);

  	/*
  	 * If the task is already exiting, don't alarm the sysadmin or kill
  	 * its children or threads, just set TIF_MEMDIE so it can die quickly
  	 */

  	if (p->flags & PF_EXITING) {

  		set_tsk_thread_flag(p, TIF_MEMDIE);

  		return 0;
  	}

  	task_lock(p);

  	pr_err("%s: Kill process %d (%s) score %d or sacrifice child
  ",

  		message, task_pid_nr(p), p->comm, points);
  	task_unlock(p);

  	/*
  	 * If any of p's children has a different mm and is eligible for kill,

  	 * the one with the highest oom_badness() score is sacrificed for its

  	 * parent.  This attempts to lose the minimal amount of work done while
  	 * still freeing memory.
  	 */

  	do {

  		list_for_each_entry(child, &t->children, sibling) {

  			unsigned int child_points;

  			if (child->mm == p->mm)
  				continue;

  			/*
  			 * oom_badness() returns 0 if the thread is unkillable
  			 */

  			child_points = oom_badness(child, memcg, nodemask,

  								totalpages);

  			if (child_points > victim_points) {
  				victim = child;
  				victim_points = child_points;
  			}

  		}
  	} while_each_thread(p, t);

  	return oom_kill_task(victim);

  }

  /*
   * Determines whether the kernel must panic because of the panic_on_oom sysctl.
   */
  static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,

  				int order, const nodemask_t *nodemask)

  {
  	if (likely(!sysctl_panic_on_oom))
  		return;
  	if (sysctl_panic_on_oom != 2) {
  		/*
  		 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
  		 * does not panic for cpuset, mempolicy, or memcg allocation
  		 * failures.
  		 */
  		if (constraint != CONSTRAINT_NONE)
  			return;
  	}
  	read_lock(&tasklist_lock);

  	dump_header(NULL, gfp_mask, order, NULL, nodemask);

  	read_unlock(&tasklist_lock);
  	panic("Out of memory: %s panic_on_oom is enabled
  ",
  		sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
  }

  #ifdef CONFIG_CGROUP_MEM_RES_CTLR

  void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask)

  {

  	unsigned long limit;
  	unsigned int points = 0;

  	struct task_struct *p;

  	/*
  	 * If current has a pending SIGKILL, then automatically select it.  The
  	 * goal is to allow it to allocate so that it may quickly exit and free
  	 * its memory.
  	 */
  	if (fatal_signal_pending(current)) {
  		set_thread_flag(TIF_MEMDIE);

  		return;
  	}

  	check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0, NULL);

  	limit = mem_cgroup_get_limit(memcg) >> PAGE_SHIFT;

  	read_lock(&tasklist_lock);

  retry:

  	p = select_bad_process(&points, limit, memcg, NULL);

  	if (!p || PTR_ERR(p) == -1UL)

  		goto out;

  	if (oom_kill_process(p, gfp_mask, 0, points, limit, memcg, NULL,

  				"Memory cgroup out of memory"))
  		goto retry;
  out:

  	read_unlock(&tasklist_lock);

  }
  #endif

  static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
  
  int register_oom_notifier(struct notifier_block *nb)
  {
  	return blocking_notifier_chain_register(&oom_notify_list, nb);
  }
  EXPORT_SYMBOL_GPL(register_oom_notifier);
  
  int unregister_oom_notifier(struct notifier_block *nb)
  {
  	return blocking_notifier_chain_unregister(&oom_notify_list, nb);
  }
  EXPORT_SYMBOL_GPL(unregister_oom_notifier);

  /*
   * Try to acquire the OOM killer lock for the zones in zonelist.  Returns zero
   * if a parallel OOM killing is already taking place that includes a zone in
   * the zonelist.  Otherwise, locks all zones in the zonelist and returns 1.
   */

  int try_set_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)

  {

  	struct zoneref *z;
  	struct zone *zone;

  	int ret = 1;

  	spin_lock(&zone_scan_lock);

  	for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
  		if (zone_is_oom_locked(zone)) {

  			ret = 0;
  			goto out;
  		}

  	}
  
  	for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
  		/*

  		 * Lock each zone in the zonelist under zone_scan_lock so a

  		 * parallel invocation of try_set_zonelist_oom() doesn't succeed

  		 * when it shouldn't.
  		 */
  		zone_set_flag(zone, ZONE_OOM_LOCKED);
  	}

  out:

  	spin_unlock(&zone_scan_lock);

  	return ret;
  }
  
  /*
   * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed
   * allocation attempts with zonelists containing them may now recall the OOM
   * killer, if necessary.
   */

  void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)

  {

  	struct zoneref *z;
  	struct zone *zone;

  	spin_lock(&zone_scan_lock);

  	for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
  		zone_clear_flag(zone, ZONE_OOM_LOCKED);
  	}

  	spin_unlock(&zone_scan_lock);

  }

  /*

   * Try to acquire the oom killer lock for all system zones.  Returns zero if a
   * parallel oom killing is taking place, otherwise locks all zones and returns
   * non-zero.
   */
  static int try_set_system_oom(void)
  {
  	struct zone *zone;
  	int ret = 1;
  
  	spin_lock(&zone_scan_lock);
  	for_each_populated_zone(zone)
  		if (zone_is_oom_locked(zone)) {
  			ret = 0;
  			goto out;
  		}
  	for_each_populated_zone(zone)
  		zone_set_flag(zone, ZONE_OOM_LOCKED);
  out:
  	spin_unlock(&zone_scan_lock);
  	return ret;
  }
  
  /*
   * Clears ZONE_OOM_LOCKED for all system zones so that failed allocation
   * attempts or page faults may now recall the oom killer, if necessary.
   */
  static void clear_system_oom(void)
  {
  	struct zone *zone;
  
  	spin_lock(&zone_scan_lock);
  	for_each_populated_zone(zone)
  		zone_clear_flag(zone, ZONE_OOM_LOCKED);
  	spin_unlock(&zone_scan_lock);
  }

  /**

   * out_of_memory - kill the "best" process when we run out of memory

   * @zonelist: zonelist pointer
   * @gfp_mask: memory allocation flags
   * @order: amount of memory being requested as a power of 2

   * @nodemask: nodemask passed to page allocator

   *
   * If we run out of memory, we have the choice between either
   * killing a random task (bad), letting the system crash (worse)
   * OR try to be smart about which process to kill. Note that we
   * don't have to be perfect here, we just have to be good.
   */

  void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
  		int order, nodemask_t *nodemask)

  {

  	const nodemask_t *mpol_mask;

  	struct task_struct *p;

  	unsigned long totalpages;

  	unsigned long freed = 0;

  	unsigned int points;

  	enum oom_constraint constraint = CONSTRAINT_NONE;

  	int killed = 0;

  
  	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
  	if (freed > 0)
  		/* Got some memory back in the last second. */
  		return;

  	/*
  	 * If current has a pending SIGKILL, then automatically select it.  The
  	 * goal is to allow it to allocate so that it may quickly exit and free
  	 * its memory.
  	 */
  	if (fatal_signal_pending(current)) {
  		set_thread_flag(TIF_MEMDIE);
  		return;
  	}

  	/*
  	 * Check if there were limitations on the allocation (only relevant for
  	 * NUMA) that may require different handling.
  	 */

  	constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
  						&totalpages);

  	mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
  	check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);

  	read_lock(&tasklist_lock);

  	if (sysctl_oom_kill_allocating_task &&

  	    !oom_unkillable_task(current, NULL, nodemask) &&

  	    current->mm) {

  		/*
  		 * oom_kill_process() needs tasklist_lock held.  If it returns
  		 * non-zero, current could not be killed so we must fallback to
  		 * the tasklist scan.
  		 */

  		if (!oom_kill_process(current, gfp_mask, order, 0, totalpages,
  				NULL, nodemask,

  				"Out of memory (oom_kill_allocating_task)"))

  			goto out;

  	}
  
  retry:

  	p = select_bad_process(&points, totalpages, NULL, mpol_mask);

  	if (PTR_ERR(p) == -1UL)

  		goto out;

  
  	/* Found nothing?!?! Either we hang forever, or we panic. */
  	if (!p) {

  		dump_header(NULL, gfp_mask, order, NULL, mpol_mask);

  		read_unlock(&tasklist_lock);
  		panic("Out of memory and no killable processes...
  ");
  	}

  	if (oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
  				nodemask, "Out of memory"))

  		goto retry;

  	killed = 1;
  out:

  	read_unlock(&tasklist_lock);

  
  	/*
  	 * Give "p" a good chance of killing itself before we

  	 * retry to allocate memory unless "p" is current

  	 */

  	if (killed && !test_thread_flag(TIF_MEMDIE))

  		schedule_timeout_uninterruptible(1);

  }

  
  /*
   * The pagefault handler calls here because it is out of memory, so kill a
   * memory-hogging task.  If a populated zone has ZONE_OOM_LOCKED set, a parallel
   * oom killing is already in progress so do nothing.  If a task is found with
   * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
   */
  void pagefault_out_of_memory(void)
  {
  	if (try_set_system_oom()) {
  		out_of_memory(NULL, 0, 0, NULL);
  		clear_system_oom();
  	}
  	if (!test_thread_flag(TIF_MEMDIE))
  		schedule_timeout_uninterruptible(1);
  }