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Message-ID: <ZA8Fizksovklmc+v@TONYMAC-ALIBABA.local>
Date: Mon, 13 Mar 2023 19:14:19 +0800
From: Tony Lu <tonylu@...ux.alibaba.com>
To: Wenjia Zhang <wenjia@...ux.ibm.com>
Cc: David Miller <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
linux-s390@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Karsten Graul <kgraul@...ux.ibm.com>,
Alexandra Winter <wintera@...ux.ibm.com>,
Jan Karcher <jaka@...ux.ibm.com>,
Stefan Raspl <raspl@...ux.ibm.com>
Subject: Re: [PATCH net 1/2] net/smc: fix deadlock triggered by
cancel_delayed_work_syn()
On Mon, Mar 13, 2023 at 11:08:28AM +0100, Wenjia Zhang wrote:
> The following LOCKDEP was detected:
> Workqueue: events smc_lgr_free_work [smc]
> WARNING: possible circular locking dependency detected
> 6.1.0-20221027.rc2.git8.56bc5b569087.300.fc36.s390x+debug #1 Not tainted
> ------------------------------------------------------
> kworker/3:0/176251 is trying to acquire lock:
> 00000000f1467148 ((wq_completion)smc_tx_wq-00000000#2){+.+.}-{0:0},
> at: __flush_workqueue+0x7a/0x4f0
> but task is already holding lock:
> 0000037fffe97dc8 ((work_completion)(&(&lgr->free_work)->work)){+.+.}-{0:0},
> at: process_one_work+0x232/0x730
> which lock already depends on the new lock.
> the existing dependency chain (in reverse order) is:
> -> #4 ((work_completion)(&(&lgr->free_work)->work)){+.+.}-{0:0}:
> __lock_acquire+0x58e/0xbd8
> lock_acquire.part.0+0xe2/0x248
> lock_acquire+0xac/0x1c8
> __flush_work+0x76/0xf0
> __cancel_work_timer+0x170/0x220
> __smc_lgr_terminate.part.0+0x34/0x1c0 [smc]
> smc_connect_rdma+0x15e/0x418 [smc]
> __smc_connect+0x234/0x480 [smc]
> smc_connect+0x1d6/0x230 [smc]
> __sys_connect+0x90/0xc0
> __do_sys_socketcall+0x186/0x370
> __do_syscall+0x1da/0x208
> system_call+0x82/0xb0
> -> #3 (smc_client_lgr_pending){+.+.}-{3:3}:
> __lock_acquire+0x58e/0xbd8
> lock_acquire.part.0+0xe2/0x248
> lock_acquire+0xac/0x1c8
> __mutex_lock+0x96/0x8e8
> mutex_lock_nested+0x32/0x40
> smc_connect_rdma+0xa4/0x418 [smc]
> __smc_connect+0x234/0x480 [smc]
> smc_connect+0x1d6/0x230 [smc]
> __sys_connect+0x90/0xc0
> __do_sys_socketcall+0x186/0x370
> __do_syscall+0x1da/0x208
> system_call+0x82/0xb0
> -> #2 (sk_lock-AF_SMC){+.+.}-{0:0}:
> __lock_acquire+0x58e/0xbd8
> lock_acquire.part.0+0xe2/0x248
> lock_acquire+0xac/0x1c8
> lock_sock_nested+0x46/0xa8
> smc_tx_work+0x34/0x50 [smc]
> process_one_work+0x30c/0x730
> worker_thread+0x62/0x420
> kthread+0x138/0x150
> __ret_from_fork+0x3c/0x58
> ret_from_fork+0xa/0x40
> -> #1 ((work_completion)(&(&smc->conn.tx_work)->work)){+.+.}-{0:0}:
> __lock_acquire+0x58e/0xbd8
> lock_acquire.part.0+0xe2/0x248
> lock_acquire+0xac/0x1c8
> process_one_work+0x2bc/0x730
> worker_thread+0x62/0x420
> kthread+0x138/0x150
> __ret_from_fork+0x3c/0x58
> ret_from_fork+0xa/0x40
> -> #0 ((wq_completion)smc_tx_wq-00000000#2){+.+.}-{0:0}:
> check_prev_add+0xd8/0xe88
> validate_chain+0x70c/0xb20
> __lock_acquire+0x58e/0xbd8
> lock_acquire.part.0+0xe2/0x248
> lock_acquire+0xac/0x1c8
> __flush_workqueue+0xaa/0x4f0
> drain_workqueue+0xaa/0x158
> destroy_workqueue+0x44/0x2d8
> smc_lgr_free+0x9e/0xf8 [smc]
> process_one_work+0x30c/0x730
> worker_thread+0x62/0x420
> kthread+0x138/0x150
> __ret_from_fork+0x3c/0x58
> ret_from_fork+0xa/0x40
> other info that might help us debug this:
> Chain exists of:
> (wq_completion)smc_tx_wq-00000000#2
> --> smc_client_lgr_pending
> --> (work_completion)(&(&lgr->free_work)->work)
> Possible unsafe locking scenario:
> CPU0 CPU1
> ---- ----
> lock((work_completion)(&(&lgr->free_work)->work));
> lock(smc_client_lgr_pending);
> lock((work_completion)
> (&(&lgr->free_work)->work));
> lock((wq_completion)smc_tx_wq-00000000#2);
> *** DEADLOCK ***
> 2 locks held by kworker/3:0/176251:
> #0: 0000000080183548
> ((wq_completion)events){+.+.}-{0:0},
> at: process_one_work+0x232/0x730
> #1: 0000037fffe97dc8
> ((work_completion)
> (&(&lgr->free_work)->work)){+.+.}-{0:0},
> at: process_one_work+0x232/0x730
> stack backtrace:
> CPU: 3 PID: 176251 Comm: kworker/3:0 Not tainted
> Hardware name: IBM 8561 T01 701 (z/VM 7.2.0)
> Call Trace:
> [<000000002983c3e4>] dump_stack_lvl+0xac/0x100
> [<0000000028b477ae>] check_noncircular+0x13e/0x160
> [<0000000028b48808>] check_prev_add+0xd8/0xe88
> [<0000000028b49cc4>] validate_chain+0x70c/0xb20
> [<0000000028b4bd26>] __lock_acquire+0x58e/0xbd8
> [<0000000028b4cf6a>] lock_acquire.part.0+0xe2/0x248
> [<0000000028b4d17c>] lock_acquire+0xac/0x1c8
> [<0000000028addaaa>] __flush_workqueue+0xaa/0x4f0
> [<0000000028addf9a>] drain_workqueue+0xaa/0x158
> [<0000000028ae303c>] destroy_workqueue+0x44/0x2d8
> [<000003ff8029af26>] smc_lgr_free+0x9e/0xf8 [smc]
> [<0000000028adf3d4>] process_one_work+0x30c/0x730
> [<0000000028adf85a>] worker_thread+0x62/0x420
> [<0000000028aeac50>] kthread+0x138/0x150
> [<0000000028a63914>] __ret_from_fork+0x3c/0x58
> [<00000000298503da>] ret_from_fork+0xa/0x40
> INFO: lockdep is turned off.
> ===================================================================
>
> This deadlock occurs because cancel_delayed_work_sync() waits for
> the work(&lgr->free_work) to finish, while the &lgr->free_work
> waits for the work(lgr->tx_wq), which needs the sk_lock-AF_SMC, that
> is already used under the mutex_lock.
>
> The solution is to use cancel_delayed_work() instead, which kills
> off a pending work.
>
> Fixes: a52bcc919b14 ("net/smc: improve termination processing")
> Signed-off-by: Wenjia Zhang <wenjia@...ux.ibm.com>
> Reviewed-by: Jan Karcher <jaka@...ux.ibm.com>
> Reviewed-by: Karsten Graul <kgraul@...ux.ibm.com>
Thanks Wenjia, LGTM.
Reviewed-by: Tony Lu <tonylu@...ux.alibaba.com>
> ---
> net/smc/smc_core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
> index d52060b2680c..454356771cda 100644
> --- a/net/smc/smc_core.c
> +++ b/net/smc/smc_core.c
> @@ -1464,7 +1464,7 @@ static void __smc_lgr_terminate(struct smc_link_group *lgr, bool soft)
> if (lgr->terminating)
> return; /* lgr already terminating */
> /* cancel free_work sync, will terminate when lgr->freeing is set */
> - cancel_delayed_work_sync(&lgr->free_work);
> + cancel_delayed_work(&lgr->free_work);
> lgr->terminating = 1;
>
> /* kill remaining link group connections */
> --
> 2.37.2
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