freezer: implement and use kthread_freezable_should_stop()
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>
diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index 7a9427e..d02b784 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -47,7 +47,7 @@
/* 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 @@
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 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) {}