Freezer: avoid freezing kernel threads prematurely
Kernel threads should not have TIF_FREEZE set when user space processes are being frozen, since otherwise some of them might be frozen prematurely. To prevent this from happening we can (1) make exit_mm() unset TIF_FREEZE unconditionally just after clearing tsk->mm and (2) make try_to_freeze_tasks() check if p->mm is different from zero and PF_BORROWED_MM is unset in p->flags when user space processes are to be frozen. Namely, when user space processes are being frozen, we only should set TIF_FREEZE for tasks that have p->mm different from NULL and don't have PF_BORROWED_MM set in p->flags. For this reason task_lock() must be used to prevent try_to_freeze_tasks() from racing with use_mm()/unuse_mm(), in which p->mm and p->flags.PF_BORROWED_MM are changed under task_lock(p). Also, we need to prevent the following scenario from happening: * daemonize() is called by a task spawned from a user space code path * freezer checks if the task has p->mm set and the result is positive * task enters exit_mm() and clears its TIF_FREEZE * freezer sets TIF_FREEZE for the task * task calls try_to_freeze() and goes to the refrigerator, which is wrong at that point This requires us to acquire task_lock(p) before p->flags.PF_BORROWED_MM and p->mm are examined and release it after TIF_FREEZE is set for p (or it turns out that TIF_FREEZE should not be set). Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Pavel Machek <pavel@ucw.cz> Cc: Nigel Cunningham <nigel@nigel.suspend2.net> Cc: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rafael J. Wysocki
Linus Torvalds
Родитель
b1457bcc3a
Коммит
0c1eecfb34
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@ -25,7 +25,7 @@ static inline int freezing(struct task_struct *p)
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/*
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* Request that a process be frozen
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*/
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static inline void freeze(struct task_struct *p)
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static inline void set_freeze_flag(struct task_struct *p)
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{
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set_tsk_thread_flag(p, TIF_FREEZE);
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}
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@ -33,7 +33,7 @@ static inline void freeze(struct task_struct *p)
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/*
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* Sometimes we may need to cancel the previous 'freeze' request
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*/
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static inline void do_not_freeze(struct task_struct *p)
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static inline void clear_freeze_flag(struct task_struct *p)
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{
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clear_tsk_thread_flag(p, TIF_FREEZE);
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}
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@ -56,7 +56,7 @@ static inline int thaw_process(struct task_struct *p)
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wake_up_process(p);
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return 1;
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}
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clear_tsk_thread_flag(p, TIF_FREEZE);
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clear_freeze_flag(p);
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task_unlock(p);
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return 0;
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}
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@ -129,7 +129,8 @@ static inline void set_freezable(void)
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#else
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static inline int frozen(struct task_struct *p) { return 0; }
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static inline int freezing(struct task_struct *p) { return 0; }
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static inline void freeze(struct task_struct *p) { BUG(); }
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static inline void set_freeze_flag(struct task_struct *p) {}
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static inline void clear_freeze_flag(struct task_struct *p) {}
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static inline int thaw_process(struct task_struct *p) { return 1; }
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static inline void refrigerator(void) {}
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@ -45,6 +45,7 @@
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#include <linux/resource.h>
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#include <linux/blkdev.h>
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#include <linux/task_io_accounting_ops.h>
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#include <linux/freezer.h>
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#include <asm/uaccess.h>
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#include <asm/unistd.h>
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@ -594,6 +595,8 @@ static void exit_mm(struct task_struct * tsk)
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tsk->mm = NULL;
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up_read(&mm->mmap_sem);
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enter_lazy_tlb(mm, current);
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/* We don't want this task to be frozen prematurely */
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clear_freeze_flag(tsk);
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task_unlock(tsk);
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mmput(mm);
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}
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@ -40,7 +40,7 @@ static inline void frozen_process(void)
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current->flags |= PF_FROZEN;
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wmb();
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}
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clear_tsk_thread_flag(current, TIF_FREEZE);
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clear_freeze_flag(current);
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}
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/* Refrigerator is place where frozen processes are stored :-). */
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@ -75,17 +75,16 @@ void refrigerator(void)
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current->state = save;
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}
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static inline void freeze_process(struct task_struct *p)
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static void freeze_task(struct task_struct *p)
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{
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unsigned long flags;
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if (!freezing(p)) {
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rmb();
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if (!frozen(p)) {
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set_freeze_flag(p);
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if (p->state == TASK_STOPPED)
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force_sig_specific(SIGSTOP, p);
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freeze(p);
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spin_lock_irqsave(&p->sighand->siglock, flags);
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signal_wake_up(p, p->state == TASK_STOPPED);
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spin_unlock_irqrestore(&p->sighand->siglock, flags);
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@ -99,18 +98,13 @@ static void cancel_freezing(struct task_struct *p)
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if (freezing(p)) {
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pr_debug(" clean up: %s\n", p->comm);
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do_not_freeze(p);
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clear_freeze_flag(p);
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spin_lock_irqsave(&p->sighand->siglock, flags);
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recalc_sigpending_and_wake(p);
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spin_unlock_irqrestore(&p->sighand->siglock, flags);
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}
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}
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static inline int is_user_space(struct task_struct *p)
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{
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return p->mm && !(p->flags & PF_BORROWED_MM);
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}
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static unsigned int try_to_freeze_tasks(int freeze_user_space)
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{
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struct task_struct *g, *p;
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@ -122,20 +116,34 @@ static unsigned int try_to_freeze_tasks(int freeze_user_space)
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todo = 0;
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read_lock(&tasklist_lock);
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do_each_thread(g, p) {
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if (!freezeable(p))
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if (frozen(p) || !freezeable(p))
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continue;
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if (frozen(p))
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continue;
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if (p->state == TASK_TRACED && frozen(p->parent)) {
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cancel_freezing(p);
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continue;
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if (freeze_user_space) {
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if (p->state == TASK_TRACED &&
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frozen(p->parent)) {
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cancel_freezing(p);
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continue;
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}
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/*
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* Kernel threads should not have TIF_FREEZE set
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* at this point, so we must ensure that either
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* p->mm is not NULL *and* PF_BORROWED_MM is
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* unset, or TIF_FRREZE is left unset.
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* The task_lock() is necessary to prevent races
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* with exit_mm() or use_mm()/unuse_mm() from
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* occuring.
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*/
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task_lock(p);
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if (!p->mm || (p->flags & PF_BORROWED_MM)) {
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task_unlock(p);
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continue;
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}
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freeze_task(p);
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task_unlock(p);
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} else {
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freeze_task(p);
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}
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if (freeze_user_space && !is_user_space(p))
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continue;
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freeze_process(p);
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if (!freezer_should_skip(p))
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todo++;
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} while_each_thread(g, p);
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@ -152,22 +160,16 @@ static unsigned int try_to_freeze_tasks(int freeze_user_space)
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* but it cleans up leftover PF_FREEZE requests.
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*/
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printk("\n");
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printk(KERN_ERR "Stopping %s timed out after %d seconds "
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printk(KERN_ERR "Freezing of %s timed out after %d seconds "
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"(%d tasks refusing to freeze):\n",
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freeze_user_space ? "user space processes" :
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"kernel threads",
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freeze_user_space ? "user space " : "tasks ",
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TIMEOUT / HZ, todo);
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show_state();
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read_lock(&tasklist_lock);
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do_each_thread(g, p) {
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if (freeze_user_space && !is_user_space(p))
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continue;
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task_lock(p);
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if (freezeable(p) && !frozen(p) &&
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!freezer_should_skip(p))
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if (freezing(p) && !freezer_should_skip(p))
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printk(KERN_ERR " %s\n", p->comm);
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cancel_freezing(p);
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task_unlock(p);
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} while_each_thread(g, p);
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@ -211,7 +213,7 @@ static void thaw_tasks(int thaw_user_space)
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if (!freezeable(p))
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continue;
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if (is_user_space(p) == !thaw_user_space)
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if (!p->mm == thaw_user_space)
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continue;
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thaw_process(p);
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