From 3664847d95e60a9a943858b7800f8484669740fc Mon Sep 17 00:00:00 2001
From: Shaohua Li <shli@fb.com>
Date: Fri, 25 Aug 2017 10:40:02 -0700
Subject: [PATCH 1/2] md/raid5: fix a race condition in stripe batch
We have a race condition in below scenario, say have 3 continuous stripes, sh1,
sh2 and sh3, sh1 is the stripe_head of sh2 and sh3:
CPU1 CPU2 CPU3
handle_stripe(sh3)
stripe_add_to_batch_list(sh3)
-> lock(sh2, sh3)
-> lock batch_lock(sh1)
-> add sh3 to batch_list of sh1
-> unlock batch_lock(sh1)
clear_batch_ready(sh1)
-> lock(sh1) and batch_lock(sh1)
-> clear STRIPE_BATCH_READY for all stripes in batch_list
-> unlock(sh1) and batch_lock(sh1)
->clear_batch_ready(sh3)
-->test_and_clear_bit(STRIPE_BATCH_READY, sh3)
--->return 0 as sh->batch == NULL
-> sh3->batch_head = sh1
-> unlock (sh2, sh3)
In CPU1, handle_stripe will continue handle sh3 even it's in batch stripe list
of sh1. By moving sh3->batch_head assignment in to batch_lock, we make it
impossible to clear STRIPE_BATCH_READY before batch_head is set.
Thanks Stephane for helping debug this tricky issue.
Reported-and-tested-by: Stephane Thiell <sthiell@stanford.edu>
Cc: stable@vger.kernel.org (v4.1+)
Signed-off-by: Shaohua Li <shli@fb.com>
---
drivers/md/raid5.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 049a958d3c1e..90414a4e0d49 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -811,6 +811,14 @@ static void stripe_add_to_batch_list(struct r5conf *conf, struct stripe_head *sh
spin_unlock(&head->batch_head->batch_lock);
goto unlock_out;
}
+ /*
+ * We must assign batch_head of this stripe within the
+ * batch_lock, otherwise clear_batch_ready of batch head
+ * stripe could clear BATCH_READY bit of this stripe and
+ * this stripe->batch_head doesn't get assigned, which
+ * could confuse clear_batch_ready for this stripe
+ */
+ sh->batch_head = head->batch_head;
/*
* at this point, head's BATCH_READY could be cleared, but we
@@ -818,8 +826,6 @@ static void stripe_add_to_batch_list(struct r5conf *conf, struct stripe_head *sh
*/
list_add(&sh->batch_list, &head->batch_list);
spin_unlock(&head->batch_head->batch_lock);
-
- sh->batch_head = head->batch_head;
} else {
head->batch_head = head;
sh->batch_head = head->batch_head;
From 184a09eb9a2fe425e49c9538f1604b05ed33cfef Mon Sep 17 00:00:00 2001
From: Dennis Yang <dennisyang@qnap.com>
Date: Wed, 6 Sep 2017 11:02:35 +0800
Subject: [PATCH 2/2] md/raid5: preserve STRIPE_ON_UNPLUG_LIST in
break_stripe_batch_list
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@qnap.com>
Cc: stable@vger.kernel.org (v4.1+)
Signed-off-by: Shaohua Li <shli@fb.com>
---
drivers/md/raid5.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 90414a4e0d49..34c01e83395a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4605,7 +4605,8 @@ static void break_stripe_batch_list(struct stripe_head *head_sh,
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;