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freezer: implement and use kthread_freezable_should_stop()

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Writeback and thinkpad_acpi have been using thaw_process() to prevent
deadlock between the freezer and kthread_stop(); unfortunately, this
is inherently racy - nothing prevents freezing from happening between
thaw_process() and kthread_stop().

This patch implements kthread_freezable_should_stop() which enters
refrigerator if necessary but is guaranteed to return if
kthread_stop() is invoked.  Both thaw_process() users are converted to
use the new function.

Note that this deadlock condition exists for many of freezable
kthreads.  They need to be converted to use the new should_stop or
freezable workqueue.

Tested with synthetic test case.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Henrique de Moraes Holschuh <ibm-acpi@hmh.eng.br>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Oleg Nesterov <oleg@redhat.com>
This commit is contained in:
Tejun Heo
2011-11-21 12:32:23 -08:00
parent a0acae0e88
commit 8a32c441c1
7 changed files with 42 additions and 23 deletions
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6
include/linux/freezer.h
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@@ -47,7 +47,7 @@ static inline bool should_send_signal(struct task_struct *p)
/* Takes and releases task alloc lock using task_lock() */
extern int thaw_process(struct task_struct *p);
extern bool __refrigerator(void);
extern bool __refrigerator(bool check_kthr_stop);
extern int freeze_processes(void);
extern int freeze_kernel_threads(void);
extern void thaw_processes(void);
@@ -57,7 +57,7 @@ static inline bool try_to_freeze(void)
might_sleep();
if (likely(!freezing(current)))
return false;
return __refrigerator();
return __refrigerator(false);
}
extern bool freeze_task(struct task_struct *p, bool sig_only);
@@ -180,7 +180,7 @@ 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 bool __refrigerator(void) { return false; }
static inline bool __refrigerator(bool check_kthr_stop) { return false; }
static inline int freeze_processes(void) { return -ENOSYS; }
static inline int freeze_kernel_threads(void) { return -ENOSYS; }
static inline void thaw_processes(void) {}