linux-kernel - Re: [PATCH] md/raid5: fix locking in handle_stripe_clean

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Date:	Fri, 30 Oct 2015 17:02:47 +0300
From:	Roman Gushchin <klamm@...dex-team.ru>
To:	Neil Brown <neilb@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	Shaohua Li <shli@...nel.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>
Subject: Re: [PATCH] md/raid5: fix locking in handle_stripe_clean_event()

> Isn't the 4.1 fix just:
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index e5befa356dbe..6e4350a78257 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -3522,16 +3522,16 @@ returnbi:
>                   * no updated data, so remove it from hash list and the stripe
>                   * will be reinitialized
>                   */
> - spin_lock_irq(&conf->device_lock);
>  unhash:
> + spin_lock_irq(conf->hash_locks + sh->hash_lock_index);
>                  remove_hash(sh);
> + spin_unlock_irq(conf->hash_locks + sh->hash_lock_index);
>                  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))
>
> ??

In my opion, this patch looks correct, although it seems to me, that there is an another issue here.

>                  if (head_sh->batch_head) {
>                          sh = list_first_entry(&sh->batch_list,
>                                                struct stripe_head, batch_list);
>                          if (sh != head_sh)
>                                          goto unhash;
>                  }
 
With a patch above this code will be executed without taking any locks. It it correct?
In my opinion, we need to take at least sh->stripe_lock, which protects sh->batch_head.
Or do I miss something?

If you want, we can handle this issue separately.


Thanks,
Roman
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