On 09/07/2012 04:08 AM, Tejun Heo wrote: >>From 985aafbf530834a9ab16348300adc7cbf35aab76 Mon Sep 17 00:00:00 2001 > From: Tejun Heo <t...@kernel.org> > Date: Thu, 6 Sep 2012 12:50:41 -0700 > > To simplify both normal and CPU hotplug paths, while CPU hotplug is in > progress, manager_mutex is held to prevent one of the workers from > becoming a manager and creating or destroying workers; unfortunately, > it currently may lead to idle worker depletion which in turn can lead > to deadlock under extreme circumstances. > > Idle workers aren't allowed to become busy if there's no other idle > worker left to create more idle workers, but during CPU_ONLINE > gcwq_associate() is holding all managerships and all the idle workers > can proceed to become busy before gcwq_associate() is finished. > > This patch fixes the bug by releasing manager_mutexes before letting > the rebound idle workers go. This ensures that by the time idle > workers check whether management is necessary, CPU_ONLINE already has > released the positions. >
Could you review manage_workers_slowpath() in V4 patchset. It has enough changelog and comments. After the discussion, We don't move the hotplug code outside hotplug code. it matches this requirement. Since we introduce manage_mutex(), any palace should be allowed to grab it when its context allows. So it is not hotplug code's responsibility of this bug. manage_workers() just use mutex_trylock() to grab the lock, it does not make hard to do it jobs when need, and it does not try to find out the reason of fail. so I think it is manage_workers()'s responsibility to handle this bug. a manage_workers_slowpath() is enough to fix the bug. ===== manage_workers_slowpath() just adds a little overhead over manage_workers(), so we can use manage_workers_slowpath() to replace manage_workers(), thus we can reduce the code of manage_workers() and we can do more cleanup for manage. Thanks, Lai -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
