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From: Muchun Song In-Reply-To: <20260617085658.27096-1-qi.zheng@linux.dev> Date: Wed, 17 Jun 2026 17:18:07 +0800 Cc: akpm@linux-foundation.org, david@fromorbit.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng , stable@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260617085658.27096-1-qi.zheng@linux.dev> To: Qi Zheng X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: D80F040011 X-Stat-Signature: tsftwduxbwzhown388bobr856hmpbx8o X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1781687951-553196 X-HE-Meta: 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 OoSDk42H 8HW/44k1D2h610Q58rjHspoGyvaLwDMUTsAQNK1ufIhrD/wagdpDUNlOGQBmSOvx1Qde5aJvdtg7gM9HuTiyAIEzPBOP3oWiEOvXJq6cLZX4kUvpfC3aBFyRcXyIsgSK/KdqPS9LAVgzYjUdHC9ykThqa+qONVyAn3VztOUjtNV7ro5YZoWAbGZweiZ30OS04+eCufwK98Pj3dw/M5mpnINoPcxZZUWboEXaQaw9cuDtFCGF86RbbICpXEa3y1jHMIiCOWxQo58xK0R10EEuqgpsi71pu69umQ0p0UiwTswpD9Da5x6OnyXMkSHP9ph8BFv/a9cVJ2tzOfKk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Jun 17, 2026, at 16:56, Qi Zheng wrote: >=20 > From: Qi Zheng >=20 > The expand_shrinker_info() iterates all visible memcgs under > shrinker_mutex, including memcgs that have not finished ->css_online() > yet. >=20 > Once pn->shrinker_info has been published, teardown must stay = serialized > with expand_shrinker_info() until that memcg is either fully online or > no longer visible to iteration. Today alloc_shrinker_info() breaks = that > rule by dropping shrinker_mutex before freeing a partially initialized > shrinker_info array, which may cause the following race: >=20 > CPU0 CPU1 > =3D=3D=3D=3D =3D=3D=3D=3D >=20 > css_create > --> list_add_tail_rcu(&css->sibling, &parent_css->children); > online_css > --> mem_cgroup_css_online > --> alloc_shrinker_info > --> alloc node0 info > rcu_assign_pointer(C->node0->shrinker_info, old0) > alloc node1 info -> FAIL -> goto err > mutex_unlock(shrinker_mutex) >=20 > shrinker_alloc() > --> shrinker_memcg_alloc > --> mutex_lock(shrinker_mutex) > expand_shrinker_info > --> mem_cgroup_iter see the memcg > expand_one_shrinker_info > --> old0 =3D C->node0->shrinker_info > memcpy(new->unit, old0->unit, = ...); >=20 > free_shrinker_info > --> kvfree(old0); >=20 > /* double free !! */ > kvfree_rcu(old0, rcu); >=20 > The same problem exists later in mem_cgroup_css_online(). If > alloc_shrinker_info() succeeds but a subsequent objcg allocation = fails, > the free_objcg -> free_shrinker_info() unwind path tears down the = already > published pn->shrinker_info arrays without shrinker_mutex. The > expand_one_shrinker_info() can race with that teardown in the same = way, > leading to use-after-free or double-free of the old shrinker_info. >=20 > Fix this by serializing shrinker_info teardown with shrinker_mutex, = and by > keeping alloc_shrinker_info() error cleanup inside the locked section. >=20 > Fixes: 307bececcd12 ("mm: shrinker: add a secondary array for = shrinker_info::{map, nr_deferred}") > Cc: stable@vger.kernel.org > Signed-off-by: Qi Zheng Acked-by: Muchun Song Thanks.