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

[Jan Kara]

Currently write(2) to a file is not interruptible by any 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). This patch makes write interruptible
by SIGKILL. We do not allow write to be interruptible by any other signal
because that has larger potential of screwing some badly written applications.

Reported-by: Kazuya Mio <k-mio@xxxxxxxxxxxxx>
Tested-by: Kazuya Mio <k-mio@xxxxxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 mm/filemap.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

  Resending this patch to allow people outside linux-fsdevel to take part
in the discussion...

diff --git a/mm/filemap.c b/mm/filemap.c
index c0018f2..c106d3b 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 +2462,10 @@ again:
 		written += copied;
 
 		balance_dirty_pages_ratelimited(mapping);
-
+		if (fatal_signal_pending(current)) {
+			status = -EINTR;
+			break;
+		}
 	} while (iov_iter_count(i));
 
 	return written ? written : status;
-- 
1.7.1

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