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/kernel/freezer.c b/kernel/freezer.c
index 732f14f..b83c30e 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -9,6 +9,7 @@
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
+#include <linux/kthread.h>
/*
* freezing is complete, mark current process as frozen
@@ -23,7 +24,7 @@
}
/* Refrigerator is place where frozen processes are stored :-). */
-bool __refrigerator(void)
+bool __refrigerator(bool check_kthr_stop)
{
/* Hmm, should we be allowed to suspend when there are realtime
processes around? */
@@ -50,7 +51,8 @@
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
- if (!frozen(current))
+ if (!frozen(current) ||
+ (check_kthr_stop && kthread_should_stop()))
break;
was_frozen = true;
schedule();