From nobody Tue Feb 10 05:43:46 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0BC83207DE2; Tue, 3 Feb 2026 08:06:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770105981; cv=none; b=FWB0fy2J533uV99Ocynf3SrjEtz2k3t3X83DRqtFuV3Ma9n8xnghvYnipeMIjoU4jNyPck0GW02urjuSBLybZP98JnzcQjajQFhO+7CBA1ju2B581gKMjThGGDNz50iSY7CdXfqKcw+MxnGh6s4+0iinKT7vYjIMiLyQaMql7/4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770105981; c=relaxed/simple; bh=zRNfVXYgulIZD3seS5ter0NjMXM16qYonEcmIcmnGMA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cK39Hp/4hX5+FmWtE+p/bsh5AlOVf6zsIeUac78zbUN26OB9dkPYIW7vv6zsdZu3WZFSfz/8YVwxJ5fZxjjfgq06fMGjCUkgOZ/ZBQVl/xQ722yOy1flvdrCa5nqN2vwArvYIFs80dKBXKmPLSEeDAIfZ87E3bh5WRD5vIw6Tm4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id E5136C116D0; Tue, 3 Feb 2026 08:06:17 +0000 (UTC) From: Yu Kuai To: tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai@fnnas.com, zhengqixing@huawei.com, mkoutny@suse.com, hch@infradead.org, ming.lei@redhat.com, nilay@linux.ibm.com Subject: [PATCH v2 4/7] blk-cgroup: skip dying blkg in blkcg_activate_policy() Date: Tue, 3 Feb 2026 16:05:59 +0800 Message-ID: <20260203080602.726505-5-yukuai@fnnas.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260203080602.726505-1-yukuai@fnnas.com> References: <20260203080602.726505-1-yukuai@fnnas.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Zheng Qixing When switching IO schedulers on a block device, blkcg_activate_policy() can race with concurrent blkcg deletion, leading to a use-after-free in rcu_accelerate_cbs. T1: T2: blkg_destroy kill(&blkg->refcnt) // blkg->refcnt=3D1->0 blkg_release // call_rcu(__blkg_release) ... blkg_free_workfn ->pd_free_fn(pd) elv_iosched_store elevator_switch ... iterate blkg list blkg_get(blkg) // blkg->refcnt=3D0->1 list_del_init(&blkg->q_node) blkg_put(pinned_blkg) // blkg->refcnt=3D1->0 blkg_release // call_rcu again rcu_accelerate_cbs // uaf Fix this by checking hlist_unhashed(&blkg->blkcg_node) before getting a reference to the blkg. This is the same check used in blkg_destroy() to detect if a blkg has already been destroyed. If the blkg is already unhashed, skip processing it since it's being destroyed. Link: https://lore.kernel.org/all/20260108014416.3656493-4-zhengqixing@huaw= eicloud.com/ Fixes: f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_w= orkfn() and blkcg_deactivate_policy()") Signed-off-by: Zheng Qixing Signed-off-by: Yu Kuai --- block/blk-cgroup.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index a6ac6ba9430d..f5b14a1d6973 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1610,6 +1610,8 @@ int blkcg_activate_policy(struct gendisk *disk, const= struct blkcg_policy *pol) =20 if (blkg->pd[pol->plid]) continue; + if (hlist_unhashed(&blkg->blkcg_node)) + continue; =20 /* If prealloc matches, use it; otherwise try GFP_NOWAIT */ if (blkg =3D=3D pinned_blkg) { --=20 2.51.0