Re: [patch 02/10 v3] raid5: delayed stripe fix

[NeilBrown <neilb@suse.de>]

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On Mon, 25 Jun 2012 15:24:49 +0800 Shaohua Li <shli@kernel.org> wrote:

> There isn't locking setting STRIPE_DELAYED and STRIPE_PREREAD_ACTIVE bits, but
> the two bits have relationship. A delayed stripe can be moved to hold list only
> when preread active stripe count is below IO_THRESHOLD. If a stripe has both
> the bits set, such stripe will be in delayed list and preread count not 0,
> which will make such stripe never leave delayed list.
> 
> Signed-off-by: Shaohua Li <shli@fusionio.com>
> ---
>  drivers/md/raid5.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Index: linux/drivers/md/raid5.c
> ===================================================================
> --- linux.orig/drivers/md/raid5.c	2012-06-25 14:36:15.964613183 +0800
> +++ linux/drivers/md/raid5.c	2012-06-25 14:36:57.280096788 +0800
> @@ -196,12 +196,14 @@ static void __release_stripe(struct r5co
>  		BUG_ON(!list_empty(&sh->lru));
>  		BUG_ON(atomic_read(&conf->active_stripes)==0);
>  		if (test_bit(STRIPE_HANDLE, &sh->state)) {
> -			if (test_bit(STRIPE_DELAYED, &sh->state))
> +			if (test_bit(STRIPE_DELAYED, &sh->state) &&
> +			    !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
>  				list_add_tail(&sh->lru, &conf->delayed_list);
>  			else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
>  				   sh->bm_seq - conf->seq_write > 0)
>  				list_add_tail(&sh->lru, &conf->bitmap_list);
>  			else {
> +				clear_bit(STRIPE_DELAYED, &sh->state);
>  				clear_bit(STRIPE_BIT_DELAY, &sh->state);
>  				list_add_tail(&sh->lru, &conf->handle_list);
>  			}

Thanks.  I've applied this patch and will submit it upstream shortly.

Have you actually seen a stripe get trapped with both bits set, or is this
just a theoretical problem discovered by code inspection?

Thanks,
NeilBrown

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