Re: [PATCH] io_uring: flush timeouts that should already have expired

[Marcelo Diop-Gonzalez <marcelo827@gmail.com>]

On Fri, Dec 18, 2020 at 11:49 AM Pavel Begunkov <asml.silence@gmail.com> wrote:
>
> On 18/12/2020 16:24, Marcelo Diop-Gonzalez wrote:
> > Right now io_flush_timeouts() checks if the current number of events
> > is equal to ->timeout.target_seq, but this will miss some timeouts if
> > there have been more than 1 event added since the last time they were
> > flushed (possible in io_submit_flush_completions(), for example). The
> > test below hangs before this change (unless you run with
> > $ ./a.out ~/somefile 1)
> >
> [...]
> >
> > Signed-off-by: Marcelo Diop-Gonzalez <marcelo827@gmail.com>
> > ---
> >  fs/io_uring.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/io_uring.c b/fs/io_uring.c
> > index b74957856e68..ae7244f8e842 100644
> > --- a/fs/io_uring.c
> > +++ b/fs/io_uring.c
> > @@ -1639,7 +1639,7 @@ static void io_flush_timeouts(struct io_ring_ctx *ctx)
> >
> >               if (io_is_timeout_noseq(req))
> >                       break;
> > -             if (req->timeout.target_seq != ctx->cached_cq_tail
> > +             if (req->timeout.target_seq > ctx->cached_cq_tail
>
> There was an pretty old patch for probably that problem, which got
> lost... Please consider that target_seq and others are u32 and may
> easily overflow, you can't do comparisons as freely. It would be
> great to finally fix it, but that can be a bit harder to do.

Ahh whoops! Good point, didn't think of that.

-Marcelo
>
> >                                       - atomic_read(&ctx->cq_timeouts))
> >                       break;
> >
> >
>
> --
> Pavel Begunkov