linux-kernel - Re: [PATCH 3/3] coredump: change wait_for_dump_helpers() to use wait_event

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Date:	Fri, 8 Mar 2013 12:22:29 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Horman <nhorman@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] coredump: change wait_for_dump_helpers() to use wait_event_interruptible()

On Fri, Mar 8, 2013 at 9:59 AM, Oleg Nesterov <oleg@...hat.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@...hat.com>

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