[PATCH 1/1] multipathd: don't leave maps read-only after write protect is cleared

[Brian Bunker <brian@purestorage.com>]

ev_add_path() sets mpp->force_readonly when a newly added path is
read-only, but never clears it. If a map is created or reloaded while
its storage is write protected, the flag stays set. When write protect
is cleared, the reload that uev_update_path() does for the DISK_RO=0
uevent uses the stale flag and loads the map read-only, even though all
of its paths are read-write. uev_update_path() clears the flag after
that reload, so the map only recovers if another DISK_RO=0 uevent
reloads it again. If none comes, the map stays read-only, and since
mpp->dmi.read_only is then 1, needs_ro_update() also ignores later
DISK_RO=1 uevents for it.

Add a helper, map_has_ro_path(), that checks whether any of a map's
paths is read-only in sysfs, and use it to set force_readonly:

- In ev_add_path(), set force_readonly from all of the map's paths
  rather than only the path being added, and clear it once the map has
  been loaded, as uev_update_path() already does after its reload. With
  need_do_map == 0 the flag is left set for the call that loads the map.

- In uev_update_path(), set force_readonly from the paths' current
  state in sysfs instead of from the uevent. The kernel updates the ro
  attribute before it sends the DISK_RO uevent, so sysfs is current
  when the uevent is handled.

- In update_map(), which does reloads that were delayed while the map
  was waiting for udev (UDEV_WAIT_RELOAD), recompute force_readonly
  before setting up the map, since the paths' state may have changed
  since it was last set.

Signed-off-by: Brian Bunker <brian@purestorage.com>
---
 multipathd/main.c | 44 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/multipathd/main.c b/multipathd/main.c
index 9bce4d6b..68916256 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -709,6 +709,22 @@ void cleanup_reset_vec(struct vector_s **v)
 	vector_reset(*v);
 }
 
+static int sysfs_get_ro(struct path *pp);
+
+/* A map must be loaded read-only if any of its paths is read-only. */
+static bool
+map_has_ro_path(struct multipath *mpp)
+{
+	struct path *pp;
+	unsigned int i;
+
+	vector_foreach_slot (mpp->paths, pp, i) {
+		if (sysfs_get_ro(pp) == 1)
+			return true;
+	}
+	return false;
+}
+
 static int
 update_map (struct multipath *mpp, struct vectors *vecs, int new_map)
 {
@@ -732,6 +748,13 @@ retry:
 
 	mpp->action = ACT_RELOAD;
 
+	/*
+	 * This may be a delayed reload, and the paths' write protect
+	 * state may have changed since force_readonly was last set.
+	 * Recompute it from the current paths.
+	 */
+	mpp->force_readonly = map_has_ro_path(mpp);
+
 	if (setup_map(mpp, &params, vecs)) {
 		condlog(0, "%s: failed to setup new map in update", mpp->alias);
 		retries = -1;
@@ -1305,7 +1328,6 @@ ev_add_path (struct path * pp, struct vectors * vecs, int need_do_map)
 	int retries = 3;
 	int start_waiter = 0;
 	int ret;
-	int ro;
 	unsigned char prflag = PR_UNSET;
 
 	/*
@@ -1370,10 +1392,11 @@ rescan:
 			goto fail; /* leave path added to pathvec */
 	}
 
-	/* ro check - if new path is ro, force map to be ro as well */
-	ro = sysfs_get_ro(pp);
-	if (ro == 1)
-		mpp->force_readonly = 1;
+	/*
+	 * Load the map read-only if any of its paths is read-only,
+	 * not just the one being added.
+	 */
+	mpp->force_readonly = map_has_ro_path(mpp);
 
 	if (!need_do_map)
 		return 0;
@@ -1400,6 +1423,8 @@ rescan:
 		sleep(1);
 		ret = domap(mpp, params, 1);
 	}
+	/* force_readonly only applies to this load, as in uev_update_path() */
+	mpp->force_readonly = 0;
 	if (ret == DOMAP_FAIL || ret == DOMAP_RETRY) {
 		condlog(0, "%s: failed in domap for addition of new "
 			"path %s", mpp->alias, pp->dev);
@@ -1732,8 +1757,13 @@ uev_update_path (struct uevent *uev, struct vectors * vecs)
 			if (mpp->wait_for_udev != UDEV_WAIT_DONE)
 				mpp->wait_for_udev = UDEV_WAIT_RELOAD;
 			else {
-				if (ro == 1)
-					pp->mpp->force_readonly = 1;
+				/*
+				 * force_readonly may be stale from ev_add_path().
+				 * Set it from the paths' current state in sysfs,
+				 * which the kernel updates before sending the
+				 * uevent, rather than from the uevent itself.
+				 */
+				pp->mpp->force_readonly = map_has_ro_path(mpp);
 				retval = reload_and_sync_map(mpp, vecs);
 				if (retval == 2)
 					condlog(2, "%s: map removed during reload", pp->dev);
-- 
2.56.0