On Thu, Jan 22, 2015 at 10:19:43AM -0500, Johannes Weiner wrote: > From 3d7ae5aeb16ce6118d8bff17194e791339a1f06c Mon Sep 17 00:00:00 2001 > From: Johannes Weiner <han...@cmpxchg.org> > Date: Thu, 22 Jan 2015 08:16:31 -0500 > Subject: [patch] kernel: cgroup: prevent mount hang due to memory controller > lifetime > > Since b2052564e66d ("mm: memcontrol: continue cache reclaim from > offlined groups"), re-mounting the memory controller after using it is > very likely to hang. > > The cgroup core assumes that any remaining references after deleting a > cgroup are temporary in nature, and synchroneously waits for them, but > the above-mentioned commit has left-over page cache pin its css until > it is reclaimed naturally. That being said, swap entries and charged > kernel memory have been doing the same indefinite pinning forever, the > bug is just more likely to trigger with left-over page cache. > > Reparenting kernel memory is highly impractical, which leaves changing > the cgroup assumptions to reflect this: once a controller has been > mounted and used, it has internal state that is independent from mount > and cgroup lifetime. It can be unmounted and remounted, but it can't > be reconfigured during subsequent mounts. > > Don't offline the controller root as long as there are any children, > dead or alive. A remount will no longer wait for these old references > to drain, it will simply mount the persistent controller state again. > > Reported-by: "Suzuki K. Poulose" <suzuki.poul...@arm.com> > Reported-by: Will Deacon <will.dea...@arm.com> > Signed-off-by: Johannes Weiner <han...@cmpxchg.org>
Applied to cgroup/for-3.19-fixes. Thanks. -- tejun -- 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/