|author||Srivatsa S. Bhat <email@example.com>||2012-01-19 23:25:33 +0100|
|committer||Rafael J. Wysocki <firstname.lastname@example.org>||2012-01-19 23:25:33 +0100|
PM / Hibernate: Rewrite unlock_system_sleep() to fix s2disk regression
Commit 33e638b, "PM / Sleep: Use the freezer_count() functions in [un]lock_system_sleep() APIs" introduced an undesirable change in the behaviour of unlock_system_sleep() since freezer_count() internally calls try_to_freeze() - which we don't need in unlock_system_sleep(). And commit bcda53f, "PM / Sleep: Replace mutex_[un]lock(&pm_mutex) with [un]lock_system_sleep()" made these APIs wide-spread. This caused a regression in suspend-to-disk where snapshot_read() and snapshot_write() were getting frozen due to the try_to_freeze embedded in unlock_system_sleep(), since these functions were invoked when the freezing condition was still in effect. Fix this by rewriting unlock_system_sleep() by open-coding freezer_count() and dropping the try_to_freeze() part. Not only will this fix the regression but this will also ensure that the API only does what it is intended to do, and nothing more, under the hood. While at it, make the code more correct and robust by ensuring that the PF_FREEZER_SKIP flag gets cleared with pm_mutex held, to avoid a race with the freezer. Also, to be on the safer side, open-code freezer_do_not_count() as well (inside lock_system_sleep()), to ensure that any unrelated modification to freezer[_do_not]_count() does not break things again! Reported-and-tested-by: Rafael J. Wysocki <email@example.com> Signed-off-by: Srivatsa S. Bhat <firstname.lastname@example.org> Acked-by: Tejun Heo <email@example.com> Signed-off-by: Rafael J. Wysocki <firstname.lastname@example.org>
1 files changed, 17 insertions, 2 deletions
diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index 95040cc33107..91784a4f8608 100644
@@ -357,14 +357,29 @@ extern bool pm_save_wakeup_count(unsigned int count);
static inline void lock_system_sleep(void)
+ current->flags |= PF_FREEZER_SKIP;
static inline void unlock_system_sleep(void)
+ * Don't use freezer_count() because we don't want the call to
+ * try_to_freeze() here.
+ * Reason:
+ * Fundamentally, we just don't need it, because freezing condition
+ * doesn't come into effect until we release the pm_mutex lock,
+ * since the freezer always works with pm_mutex held.
+ * More importantly, in the case of hibernation,
+ * unlock_system_sleep() gets called in snapshot_read() and
+ * snapshot_write() when the freezing condition is still in effect.
+ * Which means, if we use try_to_freeze() here, it would make them
+ * enter the refrigerator, thus causing hibernation to lockup.
+ current->flags &= ~PF_FREEZER_SKIP;
#else /* !CONFIG_PM_SLEEP */