linux-kernel - [PATCH 4.4 07/41] md/raid5: preserve STRIPE_ON_UNPLUG_LIST in break_stripe_batch

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Message-Id: <20171003114220.371806969@linuxfoundation.org>
Date:   Tue,  3 Oct 2017 14:21:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dennis Yang <dennisyang@...p.com>,
        Shaohua Li <shli@...com>
Subject: [PATCH 4.4 07/41] md/raid5: preserve STRIPE_ON_UNPLUG_LIST in break_stripe_batch_list

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

------------------

From: Dennis Yang <dennisyang@...p.com>

commit 184a09eb9a2fe425e49c9538f1604b05ed33cfef upstream.

In release_stripe_plug(), if a stripe_head has its STRIPE_ON_UNPLUG_LIST
set, it indicates that this stripe_head is already in the raid5_plug_cb
list and release_stripe() would be called instead to drop a reference
count. Otherwise, the STRIPE_ON_UNPLUG_LIST bit would be set for this
stripe_head and it will get queued into the raid5_plug_cb list.

Since break_stripe_batch_list() did not preserve STRIPE_ON_UNPLUG_LIST,
A stripe could be re-added to plug list while it is still on that list
in the following situation. If stripe_head A is added to another
stripe_head B's batch list, in this case A will have its
batch_head != NULL and be added into the plug list. After that,
stripe_head B gets handled and called break_stripe_batch_list() to
reset all the batched stripe_head(including A which is still on
the plug list)'s state and reset their batch_head to NULL.
Before the plug list gets processed, if there is another write request
comes in and get stripe_head A, A will have its batch_head == NULL
(cleared by calling break_stripe_batch_list() on B) and be added to
plug list once again.

Signed-off-by: Dennis Yang <dennisyang@...p.com>
Signed-off-by: Shaohua Li <shli@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/raid5.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4264,7 +4264,8 @@ static void break_stripe_batch_list(stru

 		set_mask_bits(&sh->state, ~(STRIPE_EXPAND_SYNC_FLAGS |
 					    (1 << STRIPE_PREREAD_ACTIVE) |
-					    (1 << STRIPE_DEGRADED)),
+					    (1 << STRIPE_DEGRADED) |
+					    (1 << STRIPE_ON_UNPLUG_LIST)),
 			      head_sh->state & (1 << STRIPE_INSYNC));

 		sh->check_state = head_sh->check_state;