[PATCH 3.19 156/175] md/raid5: Fix livelock when array is both resyncing and degraded.

Greg Kroah-Hartman
2015-03-04T06:22:08Z

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
@@ -3102,7 +3102,8 @@ 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
*/