LKML Archive on lore.kernel.org help / color / mirror / Atom feed
From: Pavel Begunkov <asml.silence@gmail.com> To: Nadav Amit <nadav.amit@gmail.com>, Jens Axboe <axboe@kernel.dk> Cc: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, Nadav Amit <namit@vmware.com> Subject: Re: [PATCH 1/2] io_uring: clear TIF_NOTIFY_SIGNAL when running task work Date: Sun, 8 Aug 2021 13:55:12 +0100 [thread overview] Message-ID: <488f005c-fd92-9881-2700-b2eb1adbb78e@gmail.com> (raw) In-Reply-To: <20210808001342.964634-2-namit@vmware.com> On 8/8/21 1:13 AM, Nadav Amit wrote: > From: Nadav Amit <namit@vmware.com> > > When using SQPOLL, the submission queue polling thread calls > task_work_run() to run queued work. However, when work is added with > TWA_SIGNAL - as done by io_uring itself - the TIF_NOTIFY_SIGNAL remains static int io_req_task_work_add(struct io_kiocb *req) { ... notify = (req->ctx->flags & IORING_SETUP_SQPOLL) ? TWA_NONE : TWA_SIGNAL; if (!task_work_add(tsk, &tctx->task_work, notify)) ... } io_uring doesn't set TIF_NOTIFY_SIGNAL for SQPOLL. But if you see it, I'm rather curious who does. > set afterwards and is never cleared. > > Consequently, when the submission queue polling thread checks whether > signal_pending(), it may always find a pending signal, if > task_work_add() was ever called before. > > The impact of this bug might be different on different kernel versions. > It appears that on 5.14 it would only cause unnecessary calculation and > prevent the polling thread from sleeping. On 5.13, where the bug was > found, it stops the polling thread from finding newly submitted work. > > Instead of task_work_run(), use tracehook_notify_signal() that clears > TIF_NOTIFY_SIGNAL. Test for TIF_NOTIFY_SIGNAL in addition to > current->task_works to avoid a race in which task_works is cleared but > the TIF_NOTIFY_SIGNAL is set. > > Fixes: 685fe7feedb96 ("io-wq: eliminate the need for a manager thread") > Cc: Jens Axboe <axboe@kernel.dk> > Cc: Pavel Begunkov <asml.silence@gmail.com> > Signed-off-by: Nadav Amit <namit@vmware.com> > --- > fs/io_uring.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 5a0fd6bcd318..f39244d35f90 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -78,6 +78,7 @@ > #include <linux/task_work.h> > #include <linux/pagemap.h> > #include <linux/io_uring.h> > +#include <linux/tracehook.h> > > #define CREATE_TRACE_POINTS > #include <trace/events/io_uring.h> > @@ -2203,9 +2204,9 @@ static inline unsigned int io_put_rw_kbuf(struct io_kiocb *req) > > static inline bool io_run_task_work(void) > { > - if (current->task_works) { > + if (test_thread_flag(TIF_NOTIFY_SIGNAL) || current->task_works) { > __set_current_state(TASK_RUNNING); > - task_work_run(); > + tracehook_notify_signal(); > return true; > } > > -- Pavel Begunkov
next prev parent reply other threads:[~2021-08-08 12:55 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-08-08 0:13 [PATCH 0/2] io_uring: bug fixes Nadav Amit 2021-08-08 0:13 ` [PATCH 1/2] io_uring: clear TIF_NOTIFY_SIGNAL when running task work Nadav Amit 2021-08-08 12:55 ` Pavel Begunkov [this message] 2021-08-08 17:31 ` Nadav Amit 2021-08-09 4:07 ` Hao Xu 2021-08-09 4:50 ` Nadav Amit 2021-08-09 10:35 ` Pavel Begunkov 2021-08-09 10:18 ` Pavel Begunkov 2021-08-09 21:48 ` Olivier Langlois 2021-08-10 8:28 ` Nadav Amit 2021-08-10 13:33 ` Olivier Langlois 2021-08-10 21:32 ` Pavel Begunkov 2021-08-11 2:33 ` Nadav Amit 2021-08-11 2:51 ` Jens Axboe 2021-08-11 5:40 ` I/O cancellation in io-uring (was: io_uring: clear TIF_NOTIFY_SIGNAL ...) Nadav Amit 2021-08-08 0:13 ` [PATCH 2/2] io_uring: Use WRITE_ONCE() when writing to sq_flags Nadav Amit 2021-08-09 13:53 ` [PATCH 0/2] io_uring: bug fixes Jens Axboe
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=488f005c-fd92-9881-2700-b2eb1adbb78e@gmail.com \ --to=asml.silence@gmail.com \ --cc=axboe@kernel.dk \ --cc=io-uring@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=nadav.amit@gmail.com \ --cc=namit@vmware.com \ /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: linkBe 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).