Messages in this thread | | | From | Muchun Song <> | Date | Wed, 15 Jul 2020 23:55:42 +0800 | Subject | Re: [External] Re: [PATCH v5.4.y, v4.19.y] mm: memcg/slab: fix memory leak at non-root kmem_cache destroy |
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On Wed, Jul 15, 2020 at 11:43 PM Vlastimil Babka <vbabka@suse.cz> wrote: > > On 7/15/20 5:13 PM, Muchun Song wrote: > > On Wed, Jul 15, 2020 at 7:32 PM Vlastimil Babka <vbabka@suse.cz> wrote: > >> > >> On 7/7/20 8:27 AM, Muchun Song wrote: > >> > If the kmem_cache refcount is greater than one, we should not > >> > mark the root kmem_cache as dying. If we mark the root kmem_cache > >> > dying incorrectly, the non-root kmem_cache can never be destroyed. > >> > It resulted in memory leak when memcg was destroyed. We can use the > >> > following steps to reproduce. > >> > > >> > 1) Use kmem_cache_create() to create a new kmem_cache named A. > >> > 2) Coincidentally, the kmem_cache A is an alias for kmem_cache B, > >> > so the refcount of B is just increased. > >> > 3) Use kmem_cache_destroy() to destroy the kmem_cache A, just > >> > decrease the B's refcount but mark the B as dying. > >> > 4) Create a new memory cgroup and alloc memory from the kmem_cache > >> > A. It leads to create a non-root kmem_cache for allocating. > >> > 5) When destroy the memory cgroup created in the step 4), the > >> > non-root kmem_cache can never be destroyed. > >> > > >> > If we repeat steps 4) and 5), this will cause a lot of memory leak. > >> > So only when refcount reach zero, we mark the root kmem_cache as dying. > >> > > >> > Fixes: 92ee383f6daa ("mm: fix race between kmem_cache destroy, create and deactivate") > >> > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > >> > >> CC Roman, who worked in this area recently. > >> > >> Also why is this marked "[PATCH v5.4.y, v4.19.y]"? Has it been fixed otherwise > >> in 5.5+ ? > > > > Because the memcg slab/slub is reworked by Roman since v5.8. > > That rework is in mmotm, so scheduled for 5.9, AFAIK. If you mean "The new > cgroup slab memory controller" series.
Yeah, I mean "The new cgroup slab memory controller".
> > > Therefore, this problem exists in v5.7 and below. > > Even 5.7 has a stable series, so no need to list only the LTS's. > To sum up, the patch (once reviewed) should be queued for mainline as usual, > perhaps sent before 5.8 is final, if deemed safe enough, and with added > > Cc: <stable@vger.kernel.org> > > and the Fixes: tag you provided, the applicable stable versions will pick it.
Got it. Thanks.
> > Vlastimil
-- Yours, Muchun
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