[PATCH 3.16.y-ckt 084/254] fs: make cont_expand_zero interruptible

[Luis Henriques]

3.16.7-ckt2 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka at redhat.com>

commit c2ca0fcd202863b14bd041a7fece2e789926c225 upstream.

This patch makes it possible to kill a process looping in
cont_expand_zero. A process may spend a lot of time in this function, so
it is desirable to be able to kill it.

It happened to me that I wanted to copy a piece data from the disk to a
file. By mistake, I used the "seek" parameter to dd instead of "skip". Due
to the "seek" parameter, dd attempted to extend the file and became stuck
doing so - the only possibility was to reset the machine or wait many
hours until the filesystem runs out of space and cont_expand_zero fails.
We need this patch to be able to terminate the process.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/buffer.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 19a78d074e0d..4752094053f9 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2328,6 +2328,11 @@ static int cont_expand_zero(struct file *file, struct address_space *mapping,
 		err = 0;
 
 		balance_dirty_pages_ratelimited(mapping);
+
+		if (unlikely(fatal_signal_pending(current))) {
+			err = -EINTR;
+			goto out;
+		}
 	}
 
 	/* page covers the boundary, find the boundary offset */
-- 
2.1.0