Re: [PATCH] md/raid5: fix locking in handle_stripe_clean_event()

[Luis Henriques <luis.henriques@canonical.com>]

On Fri, Nov 06, 2015 at 12:54:47PM +0300, Roman Gushchin wrote:
> commit b8a9d66d043ffac116100775a469f05f5158c16f upstream.
>

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

Cheers,
--
Lu�s


> 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
> 
> 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>
> Cc: <stable@vger.kernel.org> # 3.13 - 4.2
> ---
>  drivers/md/raid5.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index b98c70e..1c829a0 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -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
> 
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