From: Gioh Kim <gi-oh.kim@xxxxxxxxxxxxxxx>
We got a warning message below.
When server tries to close one session by force, it locks the sysfs
interface and locks the srv_sess lock.
The problem is that client can send a request to close at the same time.
By close request, server locks the srv_sess lock and locks the sysfs
to remove the sysfs interfaces.
The simplest way to prevent that situation could be just use
mutex_trylock.
[ 234.153965] ======================================================
[ 234.154093] WARNING: possible circular locking dependency detected
[ 234.154219] 5.4.84-storage #5.4.84-1+feature+linux+5.4.y+dbg+20201216.1319+b6b887b~deb10 Tainted: G O
[ 234.154381] ------------------------------------------------------
[ 234.154531] kworker/1:1H/618 is trying to acquire lock:
[ 234.154651] ffff8887a09db0a8 (kn->count#132){++++}, at: kernfs_remove_by_name_ns+0x40/0x80
[ 234.154819]
but task is already holding lock:
[ 234.154965] ffff8887ae5f6518 (&srv_sess->lock){+.+.}, at: rnbd_srv_rdma_ev+0x144/0x1590 [rnbd_server]
[ 234.155132]
which lock already depends on the new lock.
[ 234.155311]
the existing dependency chain (in reverse order) is:
[ 234.155462]
-> #1 (&srv_sess->lock){+.+.}:
[ 234.155614] __mutex_lock+0x134/0xcb0
[ 234.155761] rnbd_srv_sess_dev_force_close+0x36/0x50 [rnbd_server]
[ 234.155889] rnbd_srv_dev_session_force_close_store+0x69/0xc0 [rnbd_server]
[ 234.156042] kernfs_fop_write+0x13f/0x240
[ 234.156162] vfs_write+0xf3/0x280
[ 234.156278] ksys_write+0xba/0x150
[ 234.156395] do_syscall_64+0x62/0x270
[ 234.156513] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 234.156632]
-> #0 (kn->count#132){++++}:
[ 234.156782] __lock_acquire+0x129e/0x23a0
[ 234.156900] lock_acquire+0xf3/0x210
[ 234.157043] __kernfs_remove+0x42b/0x4c0
[ 234.157161] kernfs_remove_by_name_ns+0x40/0x80
[ 234.157282] remove_files+0x3f/0xa0
[ 234.157399] sysfs_remove_group+0x4a/0xb0
[ 234.157519] rnbd_srv_destroy_dev_session_sysfs+0x19/0x30 [rnbd_server]
[ 234.157648] rnbd_srv_rdma_ev+0x14c/0x1590 [rnbd_server]
[ 234.157775] process_io_req+0x29a/0x6a0 [rtrs_server]
[ 234.157924] __ib_process_cq+0x8c/0x100 [ib_core]
[ 234.158709] ib_cq_poll_work+0x31/0xb0 [ib_core]
[ 234.158834] process_one_work+0x4e5/0xaa0
[ 234.158958] worker_thread+0x65/0x5c0
[ 234.159078] kthread+0x1e0/0x200
[ 234.159194] ret_from_fork+0x24/0x30
[ 234.159309]
other info that might help us debug this:
[ 234.159513] Possible unsafe locking scenario:
[ 234.159658] CPU0 CPU1
[ 234.159775] ---- ----
[ 234.159891] lock(&srv_sess->lock);
[ 234.160005] lock(kn->count#132);
[ 234.160128] lock(&srv_sess->lock);
[ 234.160250] lock(kn->count#132);
[ 234.160364]
*** DEADLOCK ***
[ 234.160536] 3 locks held by kworker/1:1H/618:
[ 234.160677] #0: ffff8883ca1ed528 ((wq_completion)ib-comp-wq){+.+.}, at: process_one_work+0x40a/0xaa0
[ 234.160840] #1: ffff8883d2d5fe10 ((work_completion)(&cq->work)){+.+.}, at: process_one_work+0x40a/0xaa0
[ 234.161003] #2: ffff8887ae5f6518 (&srv_sess->lock){+.+.}, at: rnbd_srv_rdma_ev+0x144/0x1590 [rnbd_server]
[ 234.161168]
stack backtrace:
[ 234.161312] CPU: 1 PID: 618 Comm: kworker/1:1H Tainted: G O 5.4.84-storage #5.4.84-1+feature+linux+5.4.y+dbg+20201216.1319+b6b887b~deb10
[ 234.161490] Hardware name: Supermicro H8QG6/H8QG6, BIOS 3.00 09/04/2012
[ 234.161643] Workqueue: ib-comp-wq ib_cq_poll_work [ib_core]
[ 234.161765] Call Trace:
[ 234.161910] dump_stack+0x96/0xe0
[ 234.162028] check_noncircular+0x29e/0x2e0
[ 234.162148] ? print_circular_bug+0x100/0x100
[ 234.162267] ? register_lock_class+0x1ad/0x8a0
[ 234.162385] ? __lock_acquire+0x68e/0x23a0
[ 234.162505] ? trace_event_raw_event_lock+0x190/0x190
[ 234.162626] __lock_acquire+0x129e/0x23a0
[ 234.162746] ? register_lock_class+0x8a0/0x8a0
[ 234.162866] lock_acquire+0xf3/0x210
[ 234.162982] ? kernfs_remove_by_name_ns+0x40/0x80
[ 234.163127] __kernfs_remove+0x42b/0x4c0
[ 234.163243] ? kernfs_remove_by_name_ns+0x40/0x80
[ 234.163363] ? kernfs_fop_readdir+0x3b0/0x3b0
[ 234.163482] ? strlen+0x1f/0x40
[ 234.163596] ? strcmp+0x30/0x50
[ 234.163712] kernfs_remove_by_name_ns+0x40/0x80
[ 234.163832] remove_files+0x3f/0xa0
[ 234.163948] sysfs_remove_group+0x4a/0xb0
[ 234.164068] rnbd_srv_destroy_dev_session_sysfs+0x19/0x30 [rnbd_server]
[ 234.164196] rnbd_srv_rdma_ev+0x14c/0x1590 [rnbd_server]
[ 234.164345] ? _raw_spin_unlock_irqrestore+0x43/0x50
[ 234.164466] ? lockdep_hardirqs_on+0x1a8/0x290
[ 234.164597] ? mlx4_ib_poll_cq+0x927/0x1280 [mlx4_ib]
[ 234.164732] ? rnbd_get_sess_dev+0x270/0x270 [rnbd_server]
[ 234.164859] process_io_req+0x29a/0x6a0 [rtrs_server]
[ 234.164982] ? rnbd_get_sess_dev+0x270/0x270 [rnbd_server]
[ 234.165130] __ib_process_cq+0x8c/0x100 [ib_core]
[ 234.165279] ib_cq_poll_work+0x31/0xb0 [ib_core]
[ 234.165404] process_one_work+0x4e5/0xaa0
[ 234.165550] ? pwq_dec_nr_in_flight+0x160/0x160
[ 234.165675] ? do_raw_spin_lock+0x119/0x1d0
[ 234.165796] worker_thread+0x65/0x5c0
[ 234.165914] ? process_one_work+0xaa0/0xaa0
[ 234.166031] kthread+0x1e0/0x200
[ 234.166147] ? kthread_create_worker_on_cpu+0xc0/0xc0
[ 234.166268] ret_from_fork+0x24/0x30
[ 234.251591] rnbd_server L243: </dev/loop1@close_device_session>: Device closed
[ 234.604221] rnbd_server L264: RTRS Session close_device_session disconnected
Signed-off-by: Gioh Kim <gi-oh.kim@xxxxxxxxx>
Signed-off-by: Md Haris Iqbal <haris.iqbal@xxxxxxxxx>
Signed-off-by: Jack Wang <jinpu.wang@xxxxxxxxx>
---
drivers/block/rnbd/rnbd-srv.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/block/rnbd/rnbd-srv.c b/drivers/block/rnbd/rnbd-srv.c
index a4fd9f167c18..1549a6361630 100644
--- a/drivers/block/rnbd/rnbd-srv.c
+++ b/drivers/block/rnbd/rnbd-srv.c
@@ -334,7 +334,9 @@ void rnbd_srv_sess_dev_force_close(struct rnbd_srv_sess_dev *sess_dev)
struct rnbd_srv_session *sess = sess_dev->sess;
sess_dev->keep_id = true;
- mutex_lock(&sess->lock);
+ /* It is already started to close by client's close message. */
+ if (!mutex_trylock(&sess->lock))
+ return;
rnbd_srv_destroy_dev_session_sysfs(sess_dev);
mutex_unlock(&sess->lock);
}
--
2.25.1
