On Mon, Nov 21, 2011 at 11:42:54PM +0530, Srivatsa S. Bhat wrote: > The lock_system_sleep() function is used in the memory hotplug code at > several places in order to implement mutual exclusion with hibernation. > However, this function tries to acquire the 'pm_mutex' lock using > mutex_lock() and hence blocks in TASK_UNINTERRUPTIBLE state if it doesn't > get the lock. This would lead to task freezing failures and hence > hibernation failure as a consequence, even though the hibernation call path > successfully acquired the lock. > > But it is to be noted that, since this task tries to acquire pm_mutex, if it > blocks due to this, we are *100% sure* that this task is not going to run > as long as hibernation sequence is in progress, since hibernation releases > 'pm_mutex' only at the very end, when everything is done. > And this means, this task is going to be anyway blocked for much more longer > than what the freezer intends to achieve; which means, freezing and thawing > doesn't really make any difference to this task! > > So, to fix freezing failures, we just ask the freezer to skip freezing this > task, since it is already "frozen enough". > > But instead of calling freezer_do_not_count() and freezer_count() as it is, > we use only the relevant parts of those functions, because restrictions > such as 'the task should be a userspace one' etc., might not be relevant in > this scenario. > > v4: Redesigned the whole fix, to ask the freezer to skip freezing the task > which is blocked trying to acquire 'pm_mutex' lock. > > v3: Tejun suggested avoiding busy-looping by adding an msleep() since > it is not guaranteed that we will get frozen immediately. > > v2: Tejun pointed problems with using mutex_lock_interruptible() in a > while loop, when signals not related to freezing are involved. > So, replaced it with mutex_trylock(). > > Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Thanks a lot. :) -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>