From: Roman Penyaev <rpenyaev@suse.de>
To: unlisted-recipients:; (no To-header on input)
Cc: Roman Penyaev <rpenyaev@suse.de>, Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org
Subject: [PATCH 1/1] io_uring: fix infinite wait in khread_park() on io_finish_async()
Date: Mon, 13 May 2019 20:20:28 +0200 [thread overview]
Message-ID: <20190513182028.29912-1-rpenyaev@suse.de> (raw)
This fixes couple of races which lead to infinite wait of park completion
with the following backtraces:
[20801.303319] Call Trace:
[20801.303321] ? __schedule+0x284/0x650
[20801.303323] schedule+0x33/0xc0
[20801.303324] schedule_timeout+0x1bc/0x210
[20801.303326] ? schedule+0x3d/0xc0
[20801.303327] ? schedule_timeout+0x1bc/0x210
[20801.303329] ? preempt_count_add+0x79/0xb0
[20801.303330] wait_for_completion+0xa5/0x120
[20801.303331] ? wake_up_q+0x70/0x70
[20801.303333] kthread_park+0x48/0x80
[20801.303335] io_finish_async+0x2c/0x70
[20801.303336] io_ring_ctx_wait_and_kill+0x95/0x180
[20801.303338] io_uring_release+0x1c/0x20
[20801.303339] __fput+0xad/0x210
[20801.303341] task_work_run+0x8f/0xb0
[20801.303342] exit_to_usermode_loop+0xa0/0xb0
[20801.303343] do_syscall_64+0xe0/0x100
[20801.303349] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[20801.303380] Call Trace:
[20801.303383] ? __schedule+0x284/0x650
[20801.303384] schedule+0x33/0xc0
[20801.303386] io_sq_thread+0x38a/0x410
[20801.303388] ? __switch_to_asm+0x40/0x70
[20801.303390] ? wait_woken+0x80/0x80
[20801.303392] ? _raw_spin_lock_irqsave+0x17/0x40
[20801.303394] ? io_submit_sqes+0x120/0x120
[20801.303395] kthread+0x112/0x130
[20801.303396] ? kthread_create_on_node+0x60/0x60
[20801.303398] ret_from_fork+0x35/0x40
o kthread_park() waits for park completion, so io_sq_thread() loop
should check kthread_should_park() along with khread_should_stop(),
otherwise if kthread_park() is called before prepare_to_wait()
the following schedule() never returns.
o if the flag ctx->sqo_stop is observed by the io_sq_thread() loop
it is quite possible, that kthread_should_park() check and the
following kthread_parkme() is never called, because kthread_park()
has not been yet called, but few moments later is is called and
waits there for park completion, which never happens, because
kthread has already exited.
It seems that parking here is not needed at all (thread is parked and
then stopped and never unparked), so here in this patch I simply rely
on kthread_should_stop() check and then exit the thread.
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
---
fs/io_uring.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 452e35357865..449c652bb334 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -231,7 +231,6 @@ struct io_ring_ctx {
struct task_struct *sqo_thread; /* if using sq thread polling */
struct mm_struct *sqo_mm;
wait_queue_head_t sqo_wait;
- unsigned sqo_stop;
struct {
/* CQ ring */
@@ -2028,7 +2027,7 @@ static int io_sq_thread(void *data)
set_fs(USER_DS);
timeout = inflight = 0;
- while (!kthread_should_stop() && !ctx->sqo_stop) {
+ while (!kthread_should_stop()) {
bool all_fixed, mm_fault = false;
int i;
@@ -2140,9 +2139,6 @@ static int io_sq_thread(void *data)
mmput(cur_mm);
}
- if (kthread_should_park())
- kthread_parkme();
-
return 0;
}
@@ -2273,9 +2269,6 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
static void io_sq_thread_stop(struct io_ring_ctx *ctx)
{
if (ctx->sqo_thread) {
- ctx->sqo_stop = 1;
- mb();
- kthread_park(ctx->sqo_thread);
kthread_stop(ctx->sqo_thread);
ctx->sqo_thread = NULL;
}
--
2.21.0
next reply other threads:[~2019-05-13 18:20 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-13 18:20 Roman Penyaev [this message]
2019-05-13 18:25 ` [PATCH 1/1] io_uring: fix infinite wait in khread_park() on io_finish_async() Roman Penyaev
2019-05-13 18:52 ` Jens Axboe
2019-05-14 9:17 ` Roman Penyaev
2019-05-14 9:27 ` Roman Penyaev
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190513182028.29912-1-rpenyaev@suse.de \
--to=rpenyaev@suse.de \
--cc=axboe@kernel.dk \
--cc=linux-block@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).