[PATCH 3.16.y-ckt 14/58] md/raid5: fix another livelock caused by non-aligned writes.

From: Luis Henriques
Date: Thu Feb 19 2015 - 09:05:52 EST

3.16.7-ckt7 -stable review patch. If anyone has any objections, please let me know.


From: NeilBrown <neilb@xxxxxxx>

commit b1b02fe97f75b12ab34b2303bfd4e3526d903a58 upstream.

If a non-page-aligned write is destined for a device which
is missing/faulty, we can deadlock.

As the target device is missing, a read-modify-write cycle
is not possible.
As the write is not for a full-page, a recontruct-write cycle
is not possible.

This should be handled by logic in fetch_block() which notices
there is a non-R5_OVERWRITE write to a missing device, and so
loads all blocks.

However since commit 67f455486d2ea2, that code requires
STRIPE_PREREAD_ACTIVE before it will active, and those circumstances

So: in handle_stripe_dirtying, if neither rmw or rcw was possible,
set STRIPE_DELAYED, which will cause STRIPE_PREREAD_ACTIVE be set
after a suitable delay.

Fixes: 67f455486d2ea20b2d94d6adf5b9b783d079e321
Reported-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Tested-by: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
drivers/md/raid5.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 222aa7521877..68a03d7f25ee 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3204,6 +3204,11 @@ static void handle_stripe_dirtying(struct r5conf *conf,
(unsigned long long)sh->sector,
rcw, qread, test_bit(STRIPE_DELAYED, &sh->state));
+ if (rcw > disks && rmw > disks &&
+ !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+ set_bit(STRIPE_DELAYED, &sh->state);
/* now if nothing is locked, and if we have enough data,
* we can start a write request

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