[ 03/82] md: protect against crash upon fsync on ro array

Ben Hutchings
2013-03-18T04:30:57Z

From: Sebastian Riemer <sebastian.riemer@profitbricks.com>

commit bbfa57c0f2243a7c31fd248d22e9861a2802cad5 upstream.

If an fsync occurs on a read-only array, we need to send a
completion for the IO and may not increment the active IO count.
Otherwise, we hit a bug trace and can't stop the MD array anymore.

By advice of Christoph Hellwig we return success upon a flush
request but we return -EROFS for other writes.
We detect flush requests by checking if the bio has zero sectors.

This patch is suitable to any -stable kernel to which it applies.

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: NeilBrown <neilb@suse.de>
Signed-off-by: Sebastian Riemer <sebastian.riemer@profitbricks.com>
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Acked-by: Paul Menzel <paulepanter@users.sourceforge.net>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/md/md.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -345,6 +345,10 @@ static void md_make_request(struct reque
bio_io_error(bio);
return;
}
+ if (mddev->ro == 1 && unlikely(rw == WRITE)) {
+ bio_endio(bio, bio_sectors(bio) == 0 ? 0 : -EROFS);
+ return;
+ }
smp_rmb(); /* Ensure implications of 'active' are visible */
rcu_read_lock();
if (mddev->suspended) {