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authorNeilBrown <neilb@suse.de>2009-08-13 10:06:24 +1000
committerNeilBrown <neilb@suse.de>2009-08-13 10:06:24 +1000
commit67ac6011db5d2b0c853d573ff474b25c85dfb644 (patch)
tree29b30e5e4eac0564c34e0b0b3d655383ba9c783f
parent51d5668cb2e3fd1827a55184e48606fff054c5be (diff)
downloadconfigs-67ac6011db5d2b0c853d573ff474b25c85dfb644.tar.gz
md/raid5: allow new reshape modes to be restarted in the middle.
md/raid5 doesn't allow a reshape to restart if it involves writing over the same part of disk that it would be reading from. This happens at the beginning of a reshape that increases the number of devices, at the end of a reshape that decreases the number of devices, and continuously for a reshape that does not change the number of devices. The current code is correct for the "increase number of devices" case as the critical section at the start is handled by userspace performing a backup. It does not work for reducing the number of devices, or the no-change case. For 'reducing', we need to invert the test. For no-change we cannot really be sure things will be safe, so simply require the array to be read-only, which is how the user-space code which carefully starts such arrays works. Signed-off-by: NeilBrown <neilb@suse.de>
-rw-r--r--drivers/md/raid5.c21
1 files changed, 20 insertions, 1 deletions
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 2b521ee67df..b8a22a2205c 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4509,7 +4509,26 @@ static int run(mddev_t *mddev)
(old_disks-max_degraded));
/* here_old is the first stripe that we might need to read
* from */
- if (here_new >= here_old) {
+ if (mddev->delta_disks == 0) {
+ /* We cannot be sure it is safe to start an in-place
+ * reshape. It is only safe if user-space if monitoring
+ * and taking constant backups.
+ * mdadm always starts a situation like this in
+ * readonly mode so it can take control before
+ * allowing any writes. So just check for that.
+ */
+ if ((here_new * mddev->new_chunk_sectors !=
+ here_old * mddev->chunk_sectors) ||
+ mddev->ro == 0) {
+ printk(KERN_ERR "raid5: in-place reshape must be started"
+ " in read-only mode - aborting\n");
+ return -EINVAL;
+ }
+ } else if (mddev->delta_disks < 0
+ ? (here_new * mddev->new_chunk_sectors <=
+ here_old * mddev->chunk_sectors)
+ : (here_new * mddev->new_chunk_sectors >=
+ here_old * mddev->chunk_sectors)) {
/* Reading from the same stripe as writing to - bad */
printk(KERN_ERR "raid5: reshape_position too early for "
"auto-recovery - aborting.\n");