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spf=pass (imf04.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-Rspamd-Server: rspam08 X-HE-Tag: 1658933034-655847 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: [Cc Yang Shi] On Wed 27-07-22 17:07:00, tujinjiang@bytedance.com wrote: > From: Jinjiang Tu > > when shrinker is registered with SHRINKER_MEMCG_AWARE flag, > register_shrinker will not initialize shrinker->nr_deferred, > but the pointer will be passed to kfree in unregister_shrinker > when the shrinker is unregistered. This leads to kernel crash > when the shrinker object is dynamically allocated. Is this a real life problem? I thought shrinkers were pre-zeroed already. Not that we should be relying on that but it would be good to mention whether this is a code fortification or something that we should be really worried about. > To fix it, this patch initialize shrinker->nr_deferred at the > beginning of prealloc_shrinker. It would be great to add Fixes: 476b30a0949a ("mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers") > Signed-off-by: Jinjiang Tu > --- > mm/vmscan.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index f7d9a683e3a7..06ab5a398971 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -613,6 +613,7 @@ int prealloc_shrinker(struct shrinker *shrinker) > unsigned int size; > int err; > > + shrinker->nr_deferred = NULL; > if (shrinker->flags & SHRINKER_MEMCG_AWARE) { > err = prealloc_memcg_shrinker(shrinker); > if (err != -ENOSYS) You should be able to move it under SHRINKER_MEMCG_AWARE branch, no? -- Michal Hocko SUSE Labs