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SubjectRe: [PATCH 3.10 49/53] md/raid5: Fix livelock when array is both resyncing and degraded.
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Greg Kroah-Hartman <gregkh@linuxfoundation.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@redhat.com>

>
> From: NeilBrown <neilb@suse.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@amiindia.co.in>
> Bisected-by: Jes Sorensen <Jes.Sorensen@redhat.com>
> Tested-by: Jes Sorensen <Jes.Sorensen@redhat.com>
> Signed-off-by: NeilBrown <neilb@suse.de>
> Fixes: a7854487cd7128a30a7f4f5259de9f67d5efb95f
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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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