Re: INFO: task hung in io_sq_thread_stop

[Stefano Garzarella <sgarzare@redhat.com>]

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':
diff --git a/fs/io_uring.c b/fs/io_uring.c
index d00eb6bf6ce9..f35da516095a 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8649,7 +8649,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
                goto out_fput;

        if (ctx->flags & IORING_SETUP_R_DISABLED)
-               goto out_fput;
+               goto out;

        /*
         * For SQ polling, the thread will do all submissions and completions.

I'll send a patch ASAP and check if it solves this issue.

Thanks,
Stefano