[PATCH] fs: make cont_expand_zero interruptible

[Mikulas Patocka]

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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx

---
 fs/buffer.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: linux-3.14.12/fs/buffer.c
===================================================================
--- linux-3.14.12.orig/fs/buffer.c	2014-04-08 00:21:59.998849390 +0200
+++ linux-3.14.12/fs/buffer.c	2014-07-27 18:31:54.839750955 +0200
@@ -2311,6 +2311,11 @@ static int cont_expand_zero(struct file
 		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 */
--
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