Commit b1b02fe9 authored Feb 02, 2015 by NeilBrown

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 67f45548, 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: 67f45548
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>

parent 59343cd7

drivers/md/raid5.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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
		*/