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authorRafael J. Wysocki <rjw@sisk.pl>2007-07-19 12:47:33 +0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-19 21:04:42 +0400
commit0c1eecfb345401629aa57c9d3b077273e56c45a7 (patch)
tree522d7090966c6e70f3147c30e3308781e0309938 /include/linux/freezer.h
parentb1457bcc3a00a0446c7f6e2f22fd24b6d8d0a309 (diff)
downloadlinux-0c1eecfb345401629aa57c9d3b077273e56c45a7.tar.xz
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>
Diffstat (limited to 'include/linux/freezer.h')
-rw-r--r--include/linux/freezer.h9
1 files changed, 5 insertions, 4 deletions
diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index 2d38b1a74662..c8e02de737f6 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -25,7 +25,7 @@ static inline int freezing(struct task_struct *p)
/*
* Request that a process be frozen
*/
-static inline void freeze(struct task_struct *p)
+static inline void set_freeze_flag(struct task_struct *p)
{
set_tsk_thread_flag(p, TIF_FREEZE);
}
@@ -33,7 +33,7 @@ static inline void freeze(struct task_struct *p)
/*
* Sometimes we may need to cancel the previous 'freeze' request
*/
-static inline void do_not_freeze(struct task_struct *p)
+static inline void clear_freeze_flag(struct task_struct *p)
{
clear_tsk_thread_flag(p, TIF_FREEZE);
}
@@ -56,7 +56,7 @@ static inline int thaw_process(struct task_struct *p)
wake_up_process(p);
return 1;
}
- clear_tsk_thread_flag(p, TIF_FREEZE);
+ clear_freeze_flag(p);
task_unlock(p);
return 0;
}
@@ -129,7 +129,8 @@ static inline void set_freezable(void)
#else
static inline int frozen(struct task_struct *p) { return 0; }
static inline int freezing(struct task_struct *p) { return 0; }
-static inline void freeze(struct task_struct *p) { BUG(); }
+static inline void set_freeze_flag(struct task_struct *p) {}
+static inline void clear_freeze_flag(struct task_struct *p) {}
static inline int thaw_process(struct task_struct *p) { return 1; }
static inline void refrigerator(void) {}