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 <sgarzare@xxxxxxxxxx>
