From: Pavel Begunkov <asml.silence@gmail.com>
To: Hillf Danton <hdanton@sina.com>
Cc: syzbot <syzbot+c0d52d0b3c0c3ffb9525@syzkaller.appspotmail.com>,
axboe@kernel.dk, io-uring@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
peterz@infradead.org, syzkaller-bugs@googlegroups.com,
viro@zeniv.linux.org.uk, will@kernel.org
Subject: Re: INFO: task hung in __io_uring_files_cancel
Date: Mon, 23 Nov 2020 20:25:29 +0000 [thread overview]
Message-ID: <eec45499-8b3c-f17f-8d20-a3eaa4144c07@gmail.com> (raw)
In-Reply-To: <20201123073426.1951-1-hdanton@sina.com>
On 23/11/2020 07:34, Hillf Danton wrote:
[...]
> After staring the report and 311daef8013a a bit more, it seems that we
> can have a simpler fix without the help of wakeup. It is implemented
> by busy waiting until there is no more request in flight found.
I think it's better not. It doesn't happen instantly, so may take a
lot of spinning in some cases. Moreover, I don't want an unkillable
task eating up all CPU if this hangs again (eg because of some other
case).
And, I'd love to keep it working similarly to __io_uring_task_cancel()
to not think twice about all corner cases.
>
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -6077,13 +6077,10 @@ static int io_req_defer(struct io_kiocb
> static void io_req_drop_files(struct io_kiocb *req)
> {
> struct io_ring_ctx *ctx = req->ctx;
> - struct io_uring_task *tctx = req->task->io_uring;
> unsigned long flags;
>
> spin_lock_irqsave(&ctx->inflight_lock, flags);
> list_del(&req->inflight_entry);
> - if (atomic_read(&tctx->in_idle))
> - wake_up(&tctx->wait);
> spin_unlock_irqrestore(&ctx->inflight_lock, flags);
> req->flags &= ~REQ_F_INFLIGHT;
> put_files_struct(req->work.identity->files);
> @@ -8706,7 +8703,6 @@ static void io_uring_cancel_files(struct
> while (!list_empty_careful(&ctx->inflight_list)) {
> struct io_task_cancel cancel = { .task = task, .files = NULL, };
> struct io_kiocb *req;
> - DEFINE_WAIT(wait);
> bool found = false;
>
> spin_lock_irq(&ctx->inflight_lock);
> @@ -8718,9 +8714,6 @@ static void io_uring_cancel_files(struct
> found = true;
> break;
> }
> - if (found)
> - prepare_to_wait(&task->io_uring->wait, &wait,
> - TASK_UNINTERRUPTIBLE);
> spin_unlock_irq(&ctx->inflight_lock);
>
> /* We need to keep going until we don't find a matching req */
> @@ -8733,7 +8726,6 @@ static void io_uring_cancel_files(struct
> /* cancellations _may_ trigger task work */
> io_run_task_work();
> schedule();
> - finish_wait(&task->io_uring->wait, &wait);
> }
> }
>
>
--
Pavel Begunkov
next prev parent reply other threads:[~2020-11-23 20:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-21 22:35 INFO: task hung in __io_uring_files_cancel syzbot
[not found] ` <20201122030421.2088-1-hdanton@sina.com>
2020-11-22 3:32 ` Pavel Begunkov
[not found] ` <20201122092003.7724-1-hdanton@sina.com>
2020-11-22 15:57 ` Pavel Begunkov
[not found] ` <20201123073426.1951-1-hdanton@sina.com>
2020-11-23 20:25 ` Pavel Begunkov [this message]
2020-11-24 9:39 ` syzbot
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