linux-kernel - Re: [PATCH 3.10 49/53] md/raid5: Fix livelock when array is both resyncing and degraded.

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Message-ID: <wrfja8zs6ehb.fsf@ultrasam.lan.trained-monkey.org>
Date:	Wed, 04 Mar 2015 09:09:52 -0500
From:	Jes Sorensen <Jes.Sorensen@...hat.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Manibalan P <pmanibalan@...india.co.in>,
	NeilBrown <neilb@...e.de>
Subject: Re: [PATCH 3.10 49/53] md/raid5: Fix livelock when array is both resyncing and degraded.

Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:
> 3.10-stable review patch.  If anyone has any objections, please let me know.
>
> ------------------

For all 4 stable branches:

Acked-by: Jes Sorensen <Jes.Sorensen@...hat.com>

>
> From: NeilBrown <neilb@...e.de>
>
> commit 26ac107378c4742978216be1005b7291b799c7b2 upstream.
>
> Commit a7854487cd7128a30a7f4f5259de9f67d5efb95f:
>   md: When RAID5 is dirty, force reconstruct-write instead of read-modify-write.
>
> Causes an RCW cycle to be forced even when the array is degraded.
> A degraded array cannot support RCW as that requires reading all data
> blocks, and one may be missing.
>
> Forcing an RCW when it is not possible causes a live-lock and the code
> spins, repeatedly deciding to do something that cannot succeed.
>
> So change the condition to only force RCW on non-degraded arrays.
>
> Reported-by: Manibalan P <pmanibalan@...india.co.in>
> Bisected-by: Jes Sorensen <Jes.Sorensen@...hat.com>
> Tested-by: Jes Sorensen <Jes.Sorensen@...hat.com>
> Signed-off-by: NeilBrown <neilb@...e.de>
> Fixes: a7854487cd7128a30a7f4f5259de9f67d5efb95f
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> ---
>  drivers/md/raid5.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -2853,7 +2853,8 @@ static void handle_stripe_dirtying(struc
>  	 * generate correct data from the parity.
>  	 */
>  	if (conf->max_degraded == 2 ||
> -	    (recovery_cp < MaxSector && sh->sector >= recovery_cp)) {
> +	    (recovery_cp < MaxSector && sh->sector >= recovery_cp &&
> +	     s->failed == 0)) {
>  		/* Calculate the real rcw later - for now make it
>  		 * look like rcw is cheaper
>  		 */
--
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