[patch added to 3.12-stable] fs/pipe.c: skip file_update_time on frozen fs

[Jiri Slaby <jslaby@suse.cz>]

From: Dmitry Monakhov <dmonakhov@openvz.org>

This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.

===============

commit 7e775f46a125f894a1d71e96797c776dbec161f0 upstream.

Pipe has no data associated with fs so it is not good idea to block
pipe_write() if FS is frozen, but we can not update file's time on such
filesystem.  Let's use same idea as we use in touch_time().

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=65701

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 fs/pipe.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index c281867c453e..fff8057a0809 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -681,10 +681,11 @@ out:
 		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLRDNORM);
 		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 	}
-	if (ret > 0) {
+	if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
 		int err = file_update_time(filp);
 		if (err)
 			ret = err;
+		sb_end_write(file_inode(filp)->i_sb);
 	}
 	return ret;
 }
-- 
2.8.1