linux-kernel - Re: [PATCH 3/3] coredump: make wait_for_dump

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Message-ID: <CACBanvqZM-AVwwpTDW-ofi=8KH8K13jLRBzTvoB=1Mg=VPxHOQ@mail.gmail.com>
Date:	Thu, 28 Feb 2013 12:19:04 -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@...r.kernel.org
Subject: Re: [PATCH 3/3] coredump: make wait_for_dump_helpers() freezable

On Sun, Feb 24, 2013 at 9:32 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.
>
> With this change it is trivial to convert this code to use
> wait_event_freezable() and make this function freezable/killable,
> only SIGKILL can set TIF_SIGPENDING.
>
> 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.
>
> Note: wait_event_freezable() is "strange", perhaps it should be
> changed or simply removed. In the latter case we can change this
> code again to use freezer_do_not_count + wait_event_interruptible.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

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

> ---
>  fs/coredump.c |   12 ++++++------
>  1 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 4f3c8d1..284d841 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -32,6 +32,7 @@
>  #include <linux/pipe_fs_i.h>
>  #include <linux/oom.h>
>  #include <linux/compat.h>
> +#include <linux/freezer.h>
>
>  #include <asm/uaccess.h>
>  #include <asm/mmu_context.h>
> @@ -428,17 +429,16 @@ 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);
> -       }
> +       wait_event_freezable(pipe->wait, pipe->readers == 1);
>
> +       pipe_lock(pipe);
>         pipe->readers--;
>         pipe->writers++;
>         pipe_unlock(pipe);
> -
>  }
>
>  /*
> --
> 1.5.5.1
>
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