md/raid5: fix another livelock caused by non-aligned writes.

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
never set STRIPE_PREREAD_ACTIVE.

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
Cc: stable@vger.kernel.org (v3.16+)
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Tested-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c1b0d52bfcb0f7b014bbc48f4823e3b9b028dcce..b98765f6f77fd9f1e11ecdcd8809928e7b821716 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3195,6 +3195,11 @@ 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
         */