[PATCH 3/3] coredump: make wait_for_dump_helpers() freezable

[Oleg Nesterov <oleg@redhat.com>]

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@redhat.com>
---
 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