From: Wen Gu guwen@linux.alibaba.com
[ Upstream commit 7a61432dc81375be06b02f0061247d3efbdfce3a ]
Possible recursive locking is detected by lockdep when SMC falls back to TCP. The corresponding warnings are as follows:
============================================ WARNING: possible recursive locking detected 5.16.0-rc1+ #18 Tainted: G E -------------------------------------------- wrk/1391 is trying to acquire lock: ffff975246c8e7d8 (&ei->socket.wq.wait){..-.}-{3:3}, at: smc_switch_to_fallback+0x109/0x250 [smc]
but task is already holding lock: ffff975246c8f918 (&ei->socket.wq.wait){..-.}-{3:3}, at: smc_switch_to_fallback+0xfe/0x250 [smc]
other info that might help us debug this: Possible unsafe locking scenario:
CPU0 ---- lock(&ei->socket.wq.wait); lock(&ei->socket.wq.wait);
*** DEADLOCK ***
May be due to missing lock nesting notation
2 locks held by wrk/1391: #0: ffff975246040130 (sk_lock-AF_SMC){+.+.}-{0:0}, at: smc_connect+0x43/0x150 [smc] #1: ffff975246c8f918 (&ei->socket.wq.wait){..-.}-{3:3}, at: smc_switch_to_fallback+0xfe/0x250 [smc]
stack backtrace: Call Trace: <TASK> dump_stack_lvl+0x56/0x7b __lock_acquire+0x951/0x11f0 lock_acquire+0x27a/0x320 ? smc_switch_to_fallback+0x109/0x250 [smc] ? smc_switch_to_fallback+0xfe/0x250 [smc] _raw_spin_lock_irq+0x3b/0x80 ? smc_switch_to_fallback+0x109/0x250 [smc] smc_switch_to_fallback+0x109/0x250 [smc] smc_connect_fallback+0xe/0x30 [smc] __smc_connect+0xcf/0x1090 [smc] ? mark_held_locks+0x61/0x80 ? __local_bh_enable_ip+0x77/0xe0 ? lockdep_hardirqs_on+0xbf/0x130 ? smc_connect+0x12a/0x150 [smc] smc_connect+0x12a/0x150 [smc] __sys_connect+0x8a/0xc0 ? syscall_enter_from_user_mode+0x20/0x70 __x64_sys_connect+0x16/0x20 do_syscall_64+0x34/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae
The nested locking in smc_switch_to_fallback() is considered to possibly cause a deadlock because smc_wait->lock and clc_wait->lock are the same type of lock. But actually it is safe so far since there is no other place trying to obtain smc_wait->lock when clc_wait->lock is held. So the patch replaces spin_lock() with spin_lock_nested() to avoid false report by lockdep.
Link: https://lkml.org/lkml/2021/11/19/962 Fixes: 2153bd1e3d3d ("Transfer remaining wait queue entries during fallback") Reported-by: syzbot+e979d3597f48262cb4ee@syzkaller.appspotmail.com Signed-off-by: Wen Gu guwen@linux.alibaba.com Acked-by: Tony Lu tonylu@linux.alibaba.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/smc/af_smc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c index 04bf8088872a9..d324a12c26cd9 100644 --- a/net/smc/af_smc.c +++ b/net/smc/af_smc.c @@ -529,7 +529,7 @@ static void smc_switch_to_fallback(struct smc_sock *smc) * to clcsocket->wq during the fallback. */ spin_lock_irqsave(&smc_wait->lock, flags); - spin_lock(&clc_wait->lock); + spin_lock_nested(&clc_wait->lock, SINGLE_DEPTH_NESTING); list_splice_init(&smc_wait->head, &clc_wait->head); spin_unlock(&clc_wait->lock); spin_unlock_irqrestore(&smc_wait->lock, flags);