[PATCH 2/2] fs: Make write(2) interruptible by a signal

[Jan Kara <jack@suse.cz>]

Currently write(2) to a file is not interruptible by a signal. Sometimes this
is desirable (e.g. when you want to quickly kill a process hogging your disk or
when some process gets blocked in balance_dirty_pages() indefinitely due to a
filesystem being in an error condition).

Reported-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Tested-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 mm/filemap.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index c0018f2..166b30e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2407,7 +2407,6 @@ static ssize_t generic_perform_write(struct file *file,
 						iov_iter_count(i));
 
 again:
-
 		/*
 		 * Bring in the user page that we will copy from _first_.
 		 * Otherwise there's a nasty deadlock on copying from the
@@ -2463,7 +2462,15 @@ again:
 		written += copied;
 
 		balance_dirty_pages_ratelimited(mapping);
-
+		/*
+		 * We check the signal independently of balance_dirty_pages()
+		 * because we need not wait and check for signal there although
+		 * this loop could have taken significant amount of time...
+		 */
+		if (fatal_signal_pending(current)) {
+			status = -EINTR;
+			break;
+		}
 	} while (iov_iter_count(i));
 
 	return written ? written : status;
-- 
1.7.1