Re: [PATCH 3/3] coredump: change wait_for_dump_helpers() to use wait_event_interruptible()

Mandeep Singh Baines
2013-03-08T20:22:32Z

On Fri, Mar 8, 2013 at 9:59 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> wait_for_dump_helpers() calls wake_up/kill_fasync from inside the
> wait_event-like loop. This is not needed and in fact this is not
> strictly correct, we can/should do this only once after we change
> pipe->writers. We could even check if it becomes zero.
>
> Change this code to use use wait_event_interruptible(), this can
> also help to make this wait freezable.
>
> With this patch we check pipe->readers without pipe_lock(), this
> is fine. Once we see pipe->readers == 1 we know that the handler
> decremented the counter, this is all we need.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Mandeep Singh Baines <msb@chromium.org>

> ---
> fs/coredump.c | 15 +++++++++------
> 1 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 477f393..667413c 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -439,17 +439,20 @@ static void wait_for_dump_helpers(struct file *file)
> pipe_lock(pipe);
> pipe->readers++;
> pipe->writers--;
> + wake_up_interruptible_sync(&pipe->wait);
> + kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
> + pipe_unlock(pipe);
>
> - while ((pipe->readers > 1) && (!signal_pending(current))) {
> - wake_up_interruptible_sync(&pipe->wait);
> - kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
> - pipe_wait(pipe);
> - }
> + /*
> + * We actually want wait_event_freezable() but then we need
> + * to clear TIF_SIGPENDING and improve dump_interrupted().
> + */
> + wait_event_interruptible(pipe->wait, pipe->readers == 1);
>
> + pipe_lock(pipe);
> pipe->readers--;
> pipe->writers++;
> pipe_unlock(pipe);
> -
> }
>
> /*
> --
> 1.5.5.1
>