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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=tELbhXfQariElQPBOqAGKxNGlZL8E/ZXdebHFJy/Swk=; b=R2SrfE+fW8CV2h1zYgcpAF7OOx8llgJ9hSBa8sDVRiANIlZVS9h2+8vF5M/57LQvHT ajd0ecTIJnNx50QpTWy5n5lPVl3KRf5J2JbZ7TZ7nzquXX9URdfZ4JVT1pr3eF42HMPF rsXI51XutDw2w8OiuZxEzzoOE07Wms3jVvHfKYZLR8m9T4p3OKMa/qIF8U/18ooWtZeS UuuAmF9m31CuBQKPuRK3l2yx8SzLN8NPpPcxpeyMYWfjXT24IEmQnGzVmnT4x8G3YSi5 9xtFqoTfn5wwaWJS2biegVyEBBa9EdUs92WeOExrF/DnzGQLW2sg9ERONwel9nrGPZNw NayA== X-Gm-Message-State: AOAM530Fl57Ka9zBmqJBQZ4pPvxlX9nzL2Gqhg7yNS6/PVRPMvYoN2Ju aDAfHgiV9I6iaFVI/iv/EIUYwISlwdKtHMFF+IMTBw== X-Google-Smtp-Source: ABdhPJwc1+7TcV9MSi+z6TcWtLeHmWbO58lYC2oSiF2SxLlKXLntRRFRSM9/doT/IR40mAYb6sLnwqstaBc+DrKnU/M= X-Received: by 2002:ad4:414d:: with SMTP id z13mr8680267qvp.37.1604052402013; Fri, 30 Oct 2020 03:06:42 -0700 (PDT) MIME-Version: 1.0 References: <00000000000030a45905aedd879d@google.com> <20200909134317.19732-1-hdanton@sina.com> <4d55d988-d45e-ba36-fed7-342e0a6ab16e@kernel.dk> <20200909153235.joqj6hjyxug3wtwv@steredhat> In-Reply-To: <20200909153235.joqj6hjyxug3wtwv@steredhat> From: Dmitry Vyukov Date: Fri, 30 Oct 2020 11:06:30 +0100 Message-ID: Subject: Re: INFO: task hung in io_sq_thread_stop To: Stefano Garzarella Cc: Jens Axboe , Hillf Danton , syzbot , io-uring@vger.kernel.org, linux-fsdevel , LKML , Pavel Begunkov , syzkaller-bugs , Al Viro Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Wed, Sep 9, 2020 at 5:32 PM Stefano Garzarella wrote: > > On Wed, Sep 09, 2020 at 08:05:33AM -0600, Jens Axboe wrote: > > On 9/9/20 7:43 AM, Hillf Danton wrote: > > > > > > On Wed, 9 Sep 2020 12:03:55 +0200 Stefano Garzarella wrote: > > >> On Wed, Sep 09, 2020 at 01:49:22AM -0700, syzbot wrote: > > >>> Hello, > > >>> > > >>> syzbot found the following issue on: > > >>> > > >>> HEAD commit: dff9f829 Add linux-next specific files for 20200908 > > >>> git tree: linux-next > > >>> console output: https://syzkaller.appspot.com/x/log.txt?x=112f880d900000 > > >>> kernel config: https://syzkaller.appspot.com/x/.config?x=37b3426c77bda44c > > >>> dashboard link: https://syzkaller.appspot.com/bug?extid=3c23789ea938faaef049 > > >>> compiler: gcc (GCC) 10.1.0-syz 20200507 > > >>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17c082a5900000 > > >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1474f5f9900000 > > >>> > > >>> Bisection is inconclusive: the first bad commit could be any of: > > >>> > > >>> d730b1a2 io_uring: add IOURING_REGISTER_RESTRICTIONS opcode > > >>> 7ec3d1dd io_uring: allow disabling rings during the creation > > >> > > >> I'm not sure it is related, but while rebasing I forgot to update the > > >> right label in the error path. > > >> > > >> Since the check of ring state is after the increase of ctx refcount, we > > >> need to decrease it jumping to 'out' label instead of 'out_fput': > > > > > > I think we need to fix 6a7bb9ff5744 ("io_uring: remove need for > > > sqd->ctx_lock in io_sq_thread()") because the syzbot report > > > indicates the io_sq_thread has to wake up the kworker before > > > scheduling, and in turn the kworker has the chance to unpark it. > > > > > > Below is the minimum walkaround I can have because it can't > > > ensure the parker will be waken in every case. > > > > > > --- a/fs/io_uring.c > > > +++ b/fs/io_uring.c > > > @@ -6834,6 +6834,10 @@ static int io_sq_thread(void *data) > > > io_sq_thread_drop_mm(); > > > } > > > > > > + if (kthread_should_park()) { > > > + /* wake up parker before scheduling */ > > > + continue; > > > + } > > > if (ret & SQT_SPIN) { > > > io_run_task_work(); > > > cond_resched(); > > > > > > > I think this should go in the slow path: > > > > > > diff --git a/fs/io_uring.c b/fs/io_uring.c > > index 652cc53432d4..1c4fa2a0fd82 100644 > > --- a/fs/io_uring.c > > +++ b/fs/io_uring.c > > @@ -6839,6 +6839,8 @@ static int io_sq_thread(void *data) > > } else if (ret == SQT_IDLE) { > > list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) > > io_ring_set_wakeup_flag(ctx); > > + if (kthread_should_park()) > > + continue; > > schedule(); > > start_jiffies = jiffies; > > } > > > > Yes, I agree since only in this case the kthread is not rescheduled. > > Thanks both for the fix :-) > Feel free to add my R-b: > > Reviewed-by: Stefano Garzarella What happened with this fix? The bug is marked as fixed with commit "io_uring: don't sleep schedule in SQPOLL thread if we need to park": https://syzkaller.appspot.com/bug?id=d0cf0b29fc5520a8987b28f1a7b63264ae02535e But such commit cannot be found in any tree.