Messages in this thread Patch in this message | | | Date | Wed, 18 Jan 2012 22:24:36 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [Update][PATCH] PM / Hibernate: Fix s2disk regression related to unlock_system_sleep() |
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Hello Tejun,
On 01/18/2012 09:12 PM, Tejun Heo wrote:
> Hello, > > On Wed, Jan 18, 2012 at 4:59 AM, Srivatsa S. Bhat > <srivatsa.bhat@linux.vnet.ibm.com> wrote: >> + /* >> + * Don't use freezer_count() because we don't want the >> + * call to try_to_freeze() here. >> + */ > > Please explain "why" here. >
Ok, how about the following patch? ---- From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Subject: [PATCH] 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.
Reported-by: Rafael J. Wysocki <rjw@sisk.pl> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
include/linux/suspend.h | 13 ++++++++++++- 1 files changed, 12 insertions(+), 1 deletions(-)
diff --git a/include/linux/suspend.h b/include/linux/suspend.h index 95040cc..6e76380 100644 --- a/include/linux/suspend.h +++ b/include/linux/suspend.h @@ -364,7 +364,18 @@ static inline void lock_system_sleep(void) static inline void unlock_system_sleep(void) { mutex_unlock(&pm_mutex); - freezer_count(); + + /* + * Don't use freezer_count() because we don't want the call to + * try_to_freeze() here. + * + * Reason: + * 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 suspend-to-disk to lockup. + */ + current->flags &= ~PF_FREEZER_SKIP; } #else /* !CONFIG_PM_SLEEP */
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