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kernel/pid.c
12.9 KB
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// SPDX-License-Identifier: GPL-2.0-only |
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/* * Generic pidhash and scalable, time-bounded PID allocator * |
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* (C) 2002-2003 Nadia Yvette Chambers, IBM * (C) 2004 Nadia Yvette Chambers, Oracle |
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* (C) 2002-2004 Ingo Molnar, Red Hat * * pid-structures are backing objects for tasks sharing a given ID to chain * against. There is very little to them aside from hashing them and * parking tasks using given ID's on a list. * * The hash is always changed with the tasklist_lock write-acquired, * and the hash is only accessed with the tasklist_lock at least * read-acquired, so there's no additional SMP locking needed here. * * We have a list of bitmap pages, which bitmaps represent the PID space. * Allocating and freeing PIDs is completely lockless. The worst-case * allocation scenario when all but one out of 1 million PIDs possible are * allocated already: the scanning of 32 list entries and at most PAGE_SIZE * bytes. The typical fastpath is a single successful setbit. Freeing is O(1). |
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* * Pid namespaces: * (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc. * (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM * Many thanks to Oleg Nesterov for comments and help * |
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*/ #include <linux/mm.h> |
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#include <linux/export.h> |
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#include <linux/slab.h> #include <linux/init.h> |
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#include <linux/rculist.h> |
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#include <linux/memblock.h> |
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#include <linux/pid_namespace.h> |
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#include <linux/init_task.h> |
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#include <linux/syscalls.h> |
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#include <linux/proc_ns.h> |
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#include <linux/refcount.h> |
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#include <linux/anon_inodes.h> #include <linux/sched/signal.h> |
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#include <linux/sched/task.h> |
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#include <linux/idr.h> |
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|
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struct pid init_struct_pid = { |
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.count = REFCOUNT_INIT(1), |
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.tasks = { { .first = NULL }, { .first = NULL }, { .first = NULL }, }, .level = 0, .numbers = { { .nr = 0, .ns = &init_pid_ns, }, } }; |
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int pid_max = PID_MAX_DEFAULT; |
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#define RESERVED_PIDS 300 int pid_max_min = RESERVED_PIDS + 1; int pid_max_max = PID_MAX_LIMIT; |
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/* * PID-map pages start out as NULL, they get allocated upon * first use and are never deallocated. This way a low pid_max * value does not cause lots of bitmaps to be allocated, but * the scheme scales to up to 4 million PIDs, runtime. */ |
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struct pid_namespace init_pid_ns = { |
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.kref = KREF_INIT(2), |
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.idr = IDR_INIT(init_pid_ns.idr), |
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.pid_allocated = PIDNS_ADDING, |
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.level = 0, .child_reaper = &init_task, |
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.user_ns = &init_user_ns, |
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.ns.inum = PROC_PID_INIT_INO, |
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#ifdef CONFIG_PID_NS .ns.ops = &pidns_operations, #endif |
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}; |
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EXPORT_SYMBOL_GPL(init_pid_ns); |
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|
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/* * Note: disable interrupts while the pidmap_lock is held as an * interrupt might come in and do read_lock(&tasklist_lock). * * If we don't disable interrupts there is a nasty deadlock between * detach_pid()->free_pid() and another cpu that does * spin_lock(&pidmap_lock) followed by an interrupt routine that does * read_lock(&tasklist_lock); * * After we clean up the tasklist_lock and know there are no * irq handlers that take it we can leave the interrupts enabled. * For now it is easier to be safe than to prove it can't happen. */ |
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|
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static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock); |
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void put_pid(struct pid *pid) |
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{ |
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struct pid_namespace *ns; |
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if (!pid) return; |
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|
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ns = pid->numbers[pid->level].ns; |
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if (refcount_dec_and_test(&pid->count)) { |
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kmem_cache_free(ns->pid_cachep, pid); |
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put_pid_ns(ns); |
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} |
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} |
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EXPORT_SYMBOL_GPL(put_pid); |
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static void delayed_put_pid(struct rcu_head *rhp) { struct pid *pid = container_of(rhp, struct pid, rcu); put_pid(pid); } |
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void free_pid(struct pid *pid) |
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{ /* We can be called with write_lock_irq(&tasklist_lock) held */ |
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int i; |
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unsigned long flags; spin_lock_irqsave(&pidmap_lock, flags); |
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for (i = 0; i <= pid->level; i++) { struct upid *upid = pid->numbers + i; |
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struct pid_namespace *ns = upid->ns; |
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switch (--ns->pid_allocated) { |
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case 2: |
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case 1: /* When all that is left in the pid namespace * is the reaper wake up the reaper. The reaper * may be sleeping in zap_pid_ns_processes(). */ wake_up_process(ns->child_reaper); break; |
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case PIDNS_ADDING: |
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/* Handle a fork failure of the first process */ WARN_ON(ns->child_reaper); |
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ns->pid_allocated = 0; |
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/* fall through */ |
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case 0: |
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schedule_work(&ns->proc_work); break; |
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} |
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idr_remove(&ns->idr, upid->nr); |
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} |
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spin_unlock_irqrestore(&pidmap_lock, flags); |
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call_rcu(&pid->rcu, delayed_put_pid); } |
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struct pid *alloc_pid(struct pid_namespace *ns) |
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{ struct pid *pid; enum pid_type type; |
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int i, nr; struct pid_namespace *tmp; |
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struct upid *upid; |
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int retval = -ENOMEM; |
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|
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pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL); |
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if (!pid) |
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return ERR_PTR(retval); |
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|
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tmp = ns; |
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pid->level = ns->level; |
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|
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for (i = ns->level; i >= 0; i--) { |
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int pid_min = 1; idr_preload(GFP_KERNEL); spin_lock_irq(&pidmap_lock); /* * init really needs pid 1, but after reaching the maximum * wrap back to RESERVED_PIDS */ if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS) pid_min = RESERVED_PIDS; /* * Store a null pointer so find_pid_ns does not find * a partially initialized PID (see below). */ nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min, pid_max, GFP_ATOMIC); spin_unlock_irq(&pidmap_lock); idr_preload_end(); |
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if (nr < 0) { |
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retval = (nr == -ENOSPC) ? -EAGAIN : nr; |
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goto out_free; |
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} |
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|
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pid->numbers[i].nr = nr; pid->numbers[i].ns = tmp; tmp = tmp->parent; } |
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if (unlikely(is_child_reaper(pid))) { |
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if (pid_ns_prepare_proc(ns)) |
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goto out_free; } |
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get_pid_ns(ns); |
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refcount_set(&pid->count, 1); |
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for (type = 0; type < PIDTYPE_MAX; ++type) INIT_HLIST_HEAD(&pid->tasks[type]); |
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init_waitqueue_head(&pid->wait_pidfd); |
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upid = pid->numbers + ns->level; |
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spin_lock_irq(&pidmap_lock); |
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if (!(ns->pid_allocated & PIDNS_ADDING)) |
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goto out_unlock; |
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for ( ; upid >= pid->numbers; --upid) { |
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/* Make the PID visible to find_pid_ns. */ idr_replace(&upid->ns->idr, pid, upid->nr); |
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upid->ns->pid_allocated++; |
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} |
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spin_unlock_irq(&pidmap_lock); |
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return pid; |
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out_unlock: |
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spin_unlock_irq(&pidmap_lock); |
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put_pid_ns(ns); |
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out_free: |
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spin_lock_irq(&pidmap_lock); |
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while (++i <= ns->level) { upid = pid->numbers + i; idr_remove(&upid->ns->idr, upid->nr); } |
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|
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/* On failure to allocate the first pid, reset the state */ if (ns->pid_allocated == PIDNS_ADDING) idr_set_cursor(&ns->idr, 0); |
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spin_unlock_irq(&pidmap_lock); |
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|
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kmem_cache_free(ns->pid_cachep, pid); |
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return ERR_PTR(retval); |
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} |
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void disable_pid_allocation(struct pid_namespace *ns) { spin_lock_irq(&pidmap_lock); |
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ns->pid_allocated &= ~PIDNS_ADDING; |
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spin_unlock_irq(&pidmap_lock); } |
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struct pid *find_pid_ns(int nr, struct pid_namespace *ns) |
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{ |
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return idr_find(&ns->idr, nr); |
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} |
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EXPORT_SYMBOL_GPL(find_pid_ns); |
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|
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struct pid *find_vpid(int nr) { |
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return find_pid_ns(nr, task_active_pid_ns(current)); |
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} EXPORT_SYMBOL_GPL(find_vpid); |
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static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type) { return (type == PIDTYPE_PID) ? &task->thread_pid : |
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&task->signal->pids[type]; } |
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/* * attach_pid() must be called with the tasklist_lock write-held. */ |
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void attach_pid(struct task_struct *task, enum pid_type type) |
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{ |
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struct pid *pid = *task_pid_ptr(task, type); hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]); |
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} |
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static void __change_pid(struct task_struct *task, enum pid_type type, struct pid *new) |
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{ |
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struct pid **pid_ptr = task_pid_ptr(task, type); |
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struct pid *pid; int tmp; |
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|
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pid = *pid_ptr; |
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|
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hlist_del_rcu(&task->pid_links[type]); *pid_ptr = new; |
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|
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for (tmp = PIDTYPE_MAX; --tmp >= 0; ) if (!hlist_empty(&pid->tasks[tmp])) return; |
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|
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free_pid(pid); |
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} |
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void detach_pid(struct task_struct *task, enum pid_type type) { __change_pid(task, type, NULL); } void change_pid(struct task_struct *task, enum pid_type type, struct pid *pid) { __change_pid(task, type, pid); |
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attach_pid(task, type); |
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} |
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/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */ |
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void transfer_pid(struct task_struct *old, struct task_struct *new, |
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enum pid_type type) { |
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if (type == PIDTYPE_PID) new->thread_pid = old->thread_pid; hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]); |
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} |
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struct task_struct *pid_task(struct pid *pid, enum pid_type type) |
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{ |
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struct task_struct *result = NULL; if (pid) { struct hlist_node *first; |
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first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]), |
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lockdep_tasklist_lock_is_held()); |
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if (first) |
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result = hlist_entry(first, struct task_struct, pid_links[(type)]); |
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} return result; } |
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EXPORT_SYMBOL(pid_task); |
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|
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/* |
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* Must be called under rcu_read_lock(). |
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*/ |
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struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns) |
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{ |
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RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "find_task_by_pid_ns() needs rcu_read_lock() protection"); |
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return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID); |
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} |
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|
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struct task_struct *find_task_by_vpid(pid_t vnr) { |
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return find_task_by_pid_ns(vnr, task_active_pid_ns(current)); |
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} |
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|
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struct task_struct *find_get_task_by_vpid(pid_t nr) { struct task_struct *task; rcu_read_lock(); task = find_task_by_vpid(nr); if (task) get_task_struct(task); rcu_read_unlock(); return task; } |
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struct pid *get_task_pid(struct task_struct *task, enum pid_type type) { struct pid *pid; rcu_read_lock(); |
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pid = get_pid(rcu_dereference(*task_pid_ptr(task, type))); |
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rcu_read_unlock(); return pid; } |
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EXPORT_SYMBOL_GPL(get_task_pid); |
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|
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struct task_struct *get_pid_task(struct pid *pid, enum pid_type type) |
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{ struct task_struct *result; rcu_read_lock(); result = pid_task(pid, type); if (result) get_task_struct(result); rcu_read_unlock(); return result; |
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} |
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EXPORT_SYMBOL_GPL(get_pid_task); |
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|
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struct pid *find_get_pid(pid_t nr) |
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{ struct pid *pid; |
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rcu_read_lock(); |
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pid = get_pid(find_vpid(nr)); |
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rcu_read_unlock(); |
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|
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return pid; |
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} |
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EXPORT_SYMBOL_GPL(find_get_pid); |
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|
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pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns) { struct upid *upid; pid_t nr = 0; if (pid && ns->level <= pid->level) { upid = &pid->numbers[ns->level]; if (upid->ns == ns) nr = upid->nr; } return nr; } |
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EXPORT_SYMBOL_GPL(pid_nr_ns); |
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|
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pid_t pid_vnr(struct pid *pid) { |
17cf22c33 pidns: Use task_a... |
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return pid_nr_ns(pid, task_active_pid_ns(current)); |
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} EXPORT_SYMBOL_GPL(pid_vnr); |
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pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, struct pid_namespace *ns) |
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{ |
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pid_t nr = 0; rcu_read_lock(); if (!ns) |
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ns = task_active_pid_ns(current); |
2c4704756 pids: Move the pg... |
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if (likely(pid_alive(task))) nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns); |
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rcu_read_unlock(); return nr; |
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} |
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EXPORT_SYMBOL(__task_pid_nr_ns); |
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|
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struct pid_namespace *task_active_pid_ns(struct task_struct *tsk) { return ns_of_pid(task_pid(tsk)); } EXPORT_SYMBOL_GPL(task_active_pid_ns); |
1da177e4c Linux-2.6.12-rc2 |
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/* |
025dfdafe trivial: fix then... |
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* Used by proc to find the first pid that is greater than or equal to nr. |
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* |
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* If there is a pid at nr this function is exactly the same as find_pid_ns. |
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*/ |
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struct pid *find_ge_pid(int nr, struct pid_namespace *ns) |
0804ef4b0 [PATCH] proc: rea... |
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{ |
95846ecf9 pid: replace pid ... |
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return idr_get_next(&ns->idr, &nr); |
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} |
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/** * pidfd_create() - Create a new pid file descriptor. * * @pid: struct pid that the pidfd will reference * * This creates a new pid file descriptor with the O_CLOEXEC flag set. * * Note, that this function can only be called after the fd table has * been unshared to avoid leaking the pidfd to the new process. * * Return: On success, a cloexec pidfd is returned. * On error, a negative errno number will be returned. */ static int pidfd_create(struct pid *pid) { int fd; fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid), O_RDWR | O_CLOEXEC); if (fd < 0) put_pid(pid); return fd; } /** * pidfd_open() - Open new pid file descriptor. * * @pid: pid for which to retrieve a pidfd * @flags: flags to pass * * This creates a new pid file descriptor with the O_CLOEXEC flag set for * the process identified by @pid. Currently, the process identified by * @pid must be a thread-group leader. This restriction currently exists * for all aspects of pidfds including pidfd creation (CLONE_PIDFD cannot * be used with CLONE_THREAD) and pidfd polling (only supports thread group * leaders). * * Return: On success, a cloexec pidfd is returned. * On error, a negative errno number will be returned. */ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags) { int fd, ret; struct pid *p; if (flags) return -EINVAL; if (pid <= 0) return -EINVAL; p = find_get_pid(pid); if (!p) return -ESRCH; ret = 0; rcu_read_lock(); if (!pid_task(p, PIDTYPE_TGID)) ret = -EINVAL; rcu_read_unlock(); fd = ret ?: pidfd_create(p); put_pid(p); return fd; } |
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void __init pid_idr_init(void) |
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{ |
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/* Verify no one has done anything silly: */ |
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BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING); |
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|
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/* bump default and minimum pid_max based on number of cpus */ pid_max = min(pid_max_max, max_t(int, pid_max, PIDS_PER_CPU_DEFAULT * num_possible_cpus())); pid_max_min = max_t(int, pid_max_min, PIDS_PER_CPU_MIN * num_possible_cpus()); pr_info("pid_max: default: %u minimum: %u ", pid_max, pid_max_min); |
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idr_init(&init_pid_ns.idr); |
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|
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init_pid_ns.pid_cachep = KMEM_CACHE(pid, |
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SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT); |
1da177e4c Linux-2.6.12-rc2 |
511 |
} |