md/raid5: allow new reshape modes to be restarted in the middle. (67ac6011) · Commits · 戴 / test

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>

drivers/md/raid5.c

+20 −1

Original line number	Diff line number	Diff line
		@@ -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");

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