md: resolve external metadata handling deadlock in md_allow_write
md_allow_write() marks the metadata dirty while holding mddev->lock and then
waits for the write to complete. For externally managed metadata this causes a
deadlock as userspace needs to take the lock to communicate that the metadata
update has completed.
Change md_allow_write() in the 'external' case to start the 'mark active'
operation and then return -EAGAIN. The expected side effects while waiting for
userspace to write 'active' to 'array_state' are holding off reshape (code
currently handles -ENOMEM), cause some 'stripe_cache_size' change requests to
fail, cause some GET_BITMAP_FILE ioctl requests to fall back to GFP_NOIO, and
cause updates to 'raid_disks' to fail. Except for 'stripe_cache_size' changes
these failures can be mitigated by coordinating with mdmon.
md_write_start() still prevents writes from occurring until the metadata
handler has had a chance to take action as it unconditionally waits for
MD_CHANGE_CLEAN to be cleared.
[neilb@suse.de: return -EAGAIN, try GFP_NOIO]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index f05d598..491dc2d 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2136,7 +2136,7 @@
conf_t *conf = mddev_to_conf(mddev);
int cnt, raid_disks;
unsigned long flags;
- int d, d2;
+ int d, d2, err;
/* Cannot change chunk_size, layout, or level */
if (mddev->chunk_size != mddev->new_chunk ||
@@ -2148,7 +2148,9 @@
return -EINVAL;
}
- md_allow_write(mddev);
+ err = md_allow_write(mddev);
+ if (err)
+ return err;
raid_disks = mddev->raid_disks + mddev->delta_disks;