On 11/21/2011 11:53 PM, Tejun Heo wrote: > 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. :) > Thank you too :-) Regards, Srivatsa S. Bhat -- 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>