FAILED: patch "[PATCH] md/raid5: fix locking in handle_stripe_clean_event()" failed to apply to 3.14-stable tree

The patch below does not apply to the 3.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Roman Gushchin <[email protected]>
Date: Sat, 31 Oct 2015 10:53:50 +1100
Subject: [PATCH] md/raid5: fix locking in handle_stripe_clean_event()

After commit 566c09c53455 ("raid5: relieve lock contention in get_active_stripe()") __find_stripe() is called under conf->hash_locks + hash.
But handle_stripe_clean_event() calls remove_hash() under conf->device_lock.

Under some cirscumstances the hash chain can be circuited, and we get an infinite loop with disabled interrupts and locked hash lock in __find_stripe(). This leads to hard lockup on multiple CPUs and following system crash.

I was able to reproduce this behavior on raid6 over 6 ssd disks. The devices_handle_discard_safely option should be set to enable trim support. The following script was used:

for i in seq 1 32; do

    dd if=/dev/zero of=large$i bs=10M count=100 &

done

neilb: original was against a 3.x kernel. I forward-ported
to 4.3-rc. This verison is suitable for any kernel since
Commit: 59fc630b8b5f ("RAID5: batch adjacent full stripe write") (v4.1+). I'll post a version for earlier kernels to stable.

index 49bb8d3ff9be..45933c160697 100644
@@ -3499,6 +3499,7 @@ returnbi:
 		}
 	if (!discard_pending &&
 	    test_bit(R5_Discard, &sh->dev[sh->pd_idx].flags)) {
+		int hash;
 		clear_bit(R5_Discard, &sh->dev[sh->pd_idx].flags);
 		clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
 		if (sh->qd_idx >= 0) {

@@ -3512,16 +3513,17 @@ returnbi:
 		 * no updated data, so remove it from hash list and the stripe
 		 * will be reinitialized
 		 */
-		spin_lock_irq(&conf->device_lock);
 unhash:
+		hash = sh->hash_lock_index;
+		spin_lock_irq(conf->hash_locks + hash);
 		remove_hash(sh);
+		spin_unlock_irq(conf->hash_locks + hash);
 		if (head_sh->batch_head) {
 			sh = list_first_entry(&sh->batch_list,
 					      struct stripe_head, batch_list);
 			if (sh != head_sh)
 					goto unhash;
 		}
-		spin_unlock_irq(&conf->device_lock);
 		sh = head_sh;
 
 		if (test_bit(STRIPE_SYNC_REQUESTED, &sh->state))

commit b8a9d66d043ffac116100775a469f05f5158c16f upstream.

After commit 566c09c53455 ("raid5: relieve lock contention in get_active_stripe()") __find_stripe() is called under conf->hash_locks + hash.
But handle_stripe_clean_event() calls remove_hash() under conf->device_lock.

Under some cirscumstances the hash chain can be circuited, and we get an infinite loop with disabled interrupts and locked hash lock in __find_stripe(). This leads to hard lockup on multiple CPUs and following system crash.

I was able to reproduce this behavior on raid6 over 6 ssd disks. The devices_handle_discard_safely option should be set to enable trim support. The following script was used:

for i in seq 1 32; do

    dd if=/dev/zero of=large$i bs=10M count=100 &

done

---
 drivers/md/raid5.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

index b98c70e..1c829a0 100644
@@ -3029,6 +3029,8 @@ static void handle_stripe_clean_event(struct r5conf *conf,
 		}
 	if (!discard_pending &&
 	    test_bit(R5_Discard, &sh->dev[sh->pd_idx].flags)) {
+		int hash = sh->hash_lock_index;
+
 		clear_bit(R5_Discard, &sh->dev[sh->pd_idx].flags);
 		clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
 		if (sh->qd_idx >= 0) {

@@ -3042,9 +3044,9 @@ static void handle_stripe_clean_event(struct r5conf *conf,
 		 * no updated data, so remove it from hash list and the stripe
 		 * will be reinitialized
 		 */
-		spin_lock_irq(&conf->device_lock);
+		spin_lock_irq(conf->hash_locks + hash);
 		remove_hash(sh);
-		spin_unlock_irq(&conf->device_lock);
+		spin_unlock_irq(conf->hash_locks + hash);
 		if (test_bit(STRIPE_SYNC_REQUESTED, &sh->state))
 			set_bit(STRIPE_HANDLE, &sh->state);
 

2.5.0

Thanks, I'll use this backport for the 3.16 kernel as well.

Cheers,
--
Lu�s