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Fri, 20 Dec 2024 09:41:07 +0800 (CST) From: Chen Ridong To: tj@kernel.org, hannes@cmpxchg.org, longman@redhat.com, mkoutny@suse.com, roman.gushchin@linux.dev Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, chenridong@huawei.com, wangweiyang2@huawei.com Subject: [PATCH v1] cgroup/cpuset: remove kernfs active break Date: Fri, 20 Dec 2024 01:31:06 +0000 Message-Id: <20241220013106.3603227-1-chenridong@huaweicloud.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CM-TRANSID: gCh0CgDXsYUoy2Rn+5BgFA--.16396S2 X-Coremail-Antispam: 1UD129KBjvJXoWxAryrXrW5Zw1xuF1xtFyDtrb_yoWrtw18pF nxGry7Gr48Gr1UCw4DJr18Zw18t39rAFW7Jwn7Xr10va4Uuw1vyryUWrs5WrWUJry3t342 yFnxXw48tw1UAw7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUv2b4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Ar0_tr1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcxkI7VAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7MxkF7I0E n4kS14v26r1q6r43MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I 0E5I8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWU tVW8ZwCIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcV CY1x0267AKxVWUJVW8JwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAF wI0_Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa 7IU17KsUUUUUU== X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ From: Chen Ridong A warning was found: WARNING: CPU: 10 PID: 3486953 at fs/kernfs/file.c:828 CPU: 10 PID: 3486953 Comm: rmdir Kdump: loaded Tainted: G RIP: 0010:kernfs_should_drain_open_files+0x1a1/0x1b0 RSP: 0018:ffff8881107ef9e0 EFLAGS: 00010202 RAX: 0000000080000002 RBX: ffff888154738c00 RCX: dffffc0000000000 RDX: 0000000000000007 RSI: 0000000000000004 RDI: ffff888154738c04 RBP: ffff888154738c04 R08: ffffffffaf27fa15 R09: ffffed102a8e7180 R10: ffff888154738c07 R11: 0000000000000000 R12: ffff888154738c08 R13: ffff888750f8c000 R14: ffff888750f8c0e8 R15: ffff888154738ca0 FS: 00007f84cd0be740(0000) GS:ffff8887ddc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000555f9fbe00c8 CR3: 0000000153eec001 CR4: 0000000000370ee0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: kernfs_drain+0x15e/0x2f0 __kernfs_remove+0x165/0x300 kernfs_remove_by_name_ns+0x7b/0xc0 cgroup_rm_file+0x154/0x1c0 cgroup_addrm_files+0x1c2/0x1f0 css_clear_dir+0x77/0x110 kill_css+0x4c/0x1b0 cgroup_destroy_locked+0x194/0x380 cgroup_rmdir+0x2a/0x140 It can be explained by: rmdir echo 1 > cpuset.cpus kernfs_fop_write_iter // active=0 cgroup_rm_file kernfs_remove_by_name_ns kernfs_get_active // active=1 __kernfs_remove // active=0x80000002 kernfs_drain cpuset_write_resmask wait_event //waiting (active == 0x80000001) kernfs_break_active_protection // active = 0x80000001 // continue kernfs_unbreak_active_protection // active = 0x80000002 ... kernfs_should_drain_open_files // warning occurs kernfs_put_active This warning is caused by 'kernfs_break_active_protection' when it is writing to cpuset.cpus, and the cgroup is removed concurrently. The commit 3a5a6d0c2b03 ("cpuset: don't nest cgroup_mutex inside get_online_cpus()") made cpuset_hotplug_workfn asynchronous, which grabs the cgroup_mutex. To avoid deadlock. the commit 76bb5ab8f6e3 ("cpuset: break kernfs active protection in cpuset_write_resmask()") added 'kernfs_break_active_protection' in the cpuset_write_resmask. This could lead to this warning. After the commit 2125c0034c5d ("cgroup/cpuset: Make cpuset hotplug processing synchronous"), the cpuset_write_resmask no longer needs to wait the hotplug to finish, which means that cpuset_write_resmask won't grab the cgroup_mutex. So the deadlock doesn't exist anymore. Therefore, remove kernfs_break_active_protection operation in the 'cpuset_write_resmask' Fixes: 76bb5ab8f6e3 ("cpuset: break kernfs active protection in cpuset_write_resmask()") Reported-by: Ji Fa Signed-off-by: Chen Ridong --- kernel/cgroup/cpuset.c | 25 ------------------------- 1 file changed, 25 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 7ea559fb0cbf..0f910c828973 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -3124,29 +3124,6 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of, int retval = -ENODEV; buf = strstrip(buf); - - /* - * CPU or memory hotunplug may leave @cs w/o any execution - * resources, in which case the hotplug code asynchronously updates - * configuration and transfers all tasks to the nearest ancestor - * which can execute. - * - * As writes to "cpus" or "mems" may restore @cs's execution - * resources, wait for the previously scheduled operations before - * proceeding, so that we don't end up keep removing tasks added - * after execution capability is restored. - * - * cpuset_handle_hotplug may call back into cgroup core asynchronously - * via cgroup_transfer_tasks() and waiting for it from a cgroupfs - * operation like this one can lead to a deadlock through kernfs - * active_ref protection. Let's break the protection. Losing the - * protection is okay as we check whether @cs is online after - * grabbing cpuset_mutex anyway. This only happens on the legacy - * hierarchies. - */ - css_get(&cs->css); - kernfs_break_active_protection(of->kn); - cpus_read_lock(); mutex_lock(&cpuset_mutex); if (!is_cpuset_online(cs)) @@ -3179,8 +3156,6 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of, out_unlock: mutex_unlock(&cpuset_mutex); cpus_read_unlock(); - kernfs_unbreak_active_protection(of->kn); - css_put(&cs->css); flush_workqueue(cpuset_migrate_mm_wq); return retval ?: nbytes; }