linux-kernel - [PATCH 4.2 090/110] md/raid5: fix locking in handle_stripe_clean

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Message-Id: <20151106191708.716987368@linuxfoundation.org>
Date:	Fri,  6 Nov 2015 11:19:37 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Roman Gushchin <klamm@...dex-team.ru>,
	NeilBrown <neilb@...e.com>, Shaohua Li <shli@...nel.org>
Subject: [PATCH 4.2 090/110] md/raid5: fix locking in handle_stripe_clean_event()

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

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

From: Roman Gushchin <klamm@...dex-team.ru>

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

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.

Signed-off-by: Roman Gushchin <klamm@...dex-team.ru>
Fixes: 566c09c53455 ("raid5: relieve lock contention in get_active_stripe()")
Signed-off-by: NeilBrown <neilb@...e.com>
Cc: Shaohua Li <shli@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3505,6 +3505,7 @@ 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) {
@@ -3518,16 +3519,17 @@ 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))

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