[PATCH 4.1 67/86] md/raid5: fix locking in handle_stripe_clean_event()

Greg Kroah-Hartman
2015-11-06T20:02:38Z

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

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

--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3494,6 +3494,7 @@ 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) {
@@ -3507,16 +3508,17 @@ 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))