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SubjectRe: [PATCH v2 4/4] mm/slub: Fix sysfs shrink circular locking dependency
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> On Apr 27, 2020, at 7:56 PM, Waiman Long <longman@redhat.com> wrote:
>
> A lockdep splat is observed by echoing "1" to the shrink sysfs file
> and then shutting down the system:
>
> [ 167.473392] Chain exists of:
> [ 167.473392] kn->count#279 --> mem_hotplug_lock.rw_sem --> slab_mutex
> [ 167.473392]
> [ 167.484323] Possible unsafe locking scenario:
> [ 167.484323]
> [ 167.490273] CPU0 CPU1
> [ 167.494825] ---- ----
> [ 167.499376] lock(slab_mutex);
> [ 167.502530] lock(mem_hotplug_lock.rw_sem);
> [ 167.509356] lock(slab_mutex);
> [ 167.515044] lock(kn->count#279);
> [ 167.518462]
> [ 167.518462] *** DEADLOCK ***
>
> It is because of the get_online_cpus() and get_online_mems() calls in
> kmem_cache_shrink() invoked via the shrink sysfs file. To fix that, we
> have to use trylock to get the memory and cpu hotplug read locks. Since
> hotplug events are rare, it should be fine to refuse a kmem caches
> shrink operation when some hotplug events are in progress.
>
> Signed-off-by: Waiman Long <longman@redhat.com>

Feel free to use,

Reviewed-by: Qian Cai <cai@lca.pw>
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