md: remove check for MD_RECOVERY_NEEDED in action_store.

md currently doesn't allow a 'sync_action' such as 'reshape' to be set
while MD_RECOVERY_NEEDED is set.

This s a problem, particularly since commit 738a273806ee as that can
cause ->check_shape to call mddev_resume() which sets
MD_RECOVERY_NEEDED.  So by the time we come to start 'reshape' it is
very likely that MD_RECOVERY_NEEDED is still set.

Testing for this flag is not really needed and is in any case very
racy as it can be set at any moment - asynchronously.  Any race
between setting a sync_action and setting MD_RECOVERY_NEEDED must
already be handled properly in some locked code, probably
md_check_recovery(), so remove the test here.

The test on MD_RECOVERY_RUNNING is also racy in the 'reshape' case
so we should test it again after getting mddev_lock().

As this fixes a race and a regression which can cause 'reshape' to
fail, it is suitable for -stable kernels since 4.1

Reported-by: Xiao Ni <xni@redhat.com>
Fixes: 738a273806ee ("md/raid5: fix allocation of 'scribble' array.")
Cc: stable@vger.kernel.org (v4.1+)
Signed-off-by: NeilBrown <neilb@suse.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index dbedc58d8c00..61aacab424cf 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4326,8 +4326,7 @@ action_store(struct mddev *mddev, const char *page, size_t len)
                         }
                         mddev_unlock(mddev);
                 }
-        } else if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
-                   test_bit(MD_RECOVERY_NEEDED, &mddev->recovery))
+        } else if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
                 return -EBUSY;
         else if (cmd_match(page, "resync"))
                 clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
@@ -4340,8 +4339,12 @@ action_store(struct mddev *mddev, const char *page, size_t len)
                         return -EINVAL;
                 err = mddev_lock(mddev);
                 if (!err) {
-                        clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
-                        err = mddev->pers->start_reshape(mddev);
+                        if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+                                err =  -EBUSY;
+                        else {
+                                clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
+                                err = mddev->pers->start_reshape(mddev);
+                        }
                         mddev_unlock(mddev);
                 }
                 if (err)