On Sun, Feb 24, 2013 at 9:32 AM, Oleg Nesterov <o...@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.
>
> 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 <o...@redhat.com>
Acked-by: Mandeep Singh Baines <m...@chromium.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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