Ok, thank you for clarifications!
--
Roman
31.10.2015, 01:17, "Neil Brown" <neilb@xxxxxxx>:
> On Sat, Oct 31 2015, Shaohua Li wrote:
>
>> On Fri, Oct 30, 2015 at 05:02:47PM +0300, Roman Gushchin wrote:
>>> > 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.
>>
>> The batch_list list doesn't need the protection. Only the remove_hash() need it.
>
> Yes, that's my understanding too. The key to understanding is that
> comment you (helpfully!) put in clear_batch_ready():
>
> /*
> * BATCH_READY is cleared, no new stripes can be added.
> * batch_list can be accessed without lock
> */
>
> I'll wrangle some patches...
>
> Thanks,
> NeilBrown
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