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SubjectRe: [PATCH v4] mm: fix race between kmem_cache destroy, create and deactivate
On Mon, Jun 11, 2018 at 12:29:51PM -0700, Shakeel Butt wrote:
> The memcg kmem cache creation and deactivation (SLUB only) is
> asynchronous. If a root kmem cache is destroyed whose memcg cache is in
> the process of creation or deactivation, the kernel may crash.
>
> Example of one such crash:
> general protection fault: 0000 [#1] SMP PTI
> CPU: 1 PID: 1721 Comm: kworker/14:1 Not tainted 4.17.0-smp
> ...
> Workqueue: memcg_kmem_cache kmemcg_deactivate_workfn
> RIP: 0010:has_cpu_slab
> ...
> Call Trace:
> ? on_each_cpu_cond
> __kmem_cache_shrink
> kmemcg_cache_deact_after_rcu
> kmemcg_deactivate_workfn
> process_one_work
> worker_thread
> kthread
> ret_from_fork+0x35/0x40
>
> To fix this race, on root kmem cache destruction, mark the cache as
> dying and flush the workqueue used for memcg kmem cache creation and
> deactivation. SLUB's memcg kmem cache deactivation also includes RCU
> callback and thus make sure all previous registered RCU callbacks
> have completed as well.
>
> Signed-off-by: Shakeel Butt <shakeelb@google.com>

Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>

Thanks.

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