This is a note to let you know that I've just added the patch titled
net/smc: Prevent smc_release() from long blocking
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-smc-prevent-smc_release-from-long-blocking.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4f74f2327c0800885bbbe3253a86dac33ddf47a5
Author: D. Wythe <alibuda@xxxxxxxxxxxxxxxxx>
Date: Wed Dec 15 20:29:21 2021 +0800
net/smc: Prevent smc_release() from long blocking
[ Upstream commit 5c15b3123f65f8fbb1b445d9a7e8812e0e435df2 ]
In nginx/wrk benchmark, there's a hung problem with high probability
on case likes that: (client will last several minutes to exit)
server: smc_run nginx
client: smc_run wrk -c 10000 -t 1 http://server
Client hangs with the following backtrace:
0 [ffffa7ce8Of3bbf8] __schedule at ffffffff9f9eOd5f
1 [ffffa7ce8Of3bc88] schedule at ffffffff9f9eløe6
2 [ffffa7ce8Of3bcaO] schedule_timeout at ffffffff9f9e3f3c
3 [ffffa7ce8Of3bd2O] wait_for_common at ffffffff9f9el9de
4 [ffffa7ce8Of3bd8O] __flush_work at ffffffff9fOfeOl3
5 [ffffa7ce8øf3bdfO] smc_release at ffffffffcO697d24 [smc]
6 [ffffa7ce8Of3be2O] __sock_release at ffffffff9f8O2e2d
7 [ffffa7ce8Of3be4ø] sock_close at ffffffff9f8ø2ebl
8 [ffffa7ce8øf3be48] __fput at ffffffff9f334f93
9 [ffffa7ce8Of3be78] task_work_run at ffffffff9flOlff5
10 [ffffa7ce8Of3beaO] do_exit at ffffffff9fOe5Ol2
11 [ffffa7ce8Of3bflO] do_group_exit at ffffffff9fOe592a
12 [ffffa7ce8Of3bf38] __x64_sys_exit_group at ffffffff9fOe5994
13 [ffffa7ce8Of3bf4O] do_syscall_64 at ffffffff9f9d4373
14 [ffffa7ce8Of3bfsO] entry_SYSCALL_64_after_hwframe at ffffffff9fa0007c
This issue dues to flush_work(), which is used to wait for
smc_connect_work() to finish in smc_release(). Once lots of
smc_connect_work() was pending or all executing work dangling,
smc_release() has to block until one worker comes to free, which
is equivalent to wait another smc_connnect_work() to finish.
In order to fix this, There are two changes:
1. For those idle smc_connect_work(), cancel it from the workqueue; for
executing smc_connect_work(), waiting for it to finish. For that
purpose, replace flush_work() with cancel_work_sync().
2. Since smc_connect() hold a reference for passive closing, if
smc_connect_work() has been cancelled, release the reference.
Fixes: 24ac3a08e658 ("net/smc: rebuild nonblocking connect")
Reported-by: Tony Lu <tonylu@xxxxxxxxxxxxxxxxx>
Tested-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
Reviewed-by: Tony Lu <tonylu@xxxxxxxxxxxxxxxxx>
Signed-off-by: D. Wythe <alibuda@xxxxxxxxxxxxxxxxx>
Acked-by: Karsten Graul <kgraul@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1639571361-101128-1-git-send-email-alibuda@xxxxxxxxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index fa3b20e5f4608..06684ac346abd 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -183,7 +183,9 @@ static int smc_release(struct socket *sock)
/* cleanup for a dangling non-blocking connect */
if (smc->connect_nonblock && sk->sk_state == SMC_INIT)
tcp_abort(smc->clcsock->sk, ECONNABORTED);
- flush_work(&smc->connect_work);
+
+ if (cancel_work_sync(&smc->connect_work))
+ sock_put(&smc->sk); /* sock_hold in smc_connect for passive closing */
if (sk->sk_state == SMC_LISTEN)
/* smc_close_non_accepted() is called and acquires
