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

Oleg Nesterov
2013-03-08T18:01:19Z

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>
---
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