On Thu, Oct 22, 2026 at 04:48:53PM -0700, Brian Bunker wrote:
> 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.
>
> Fix this by setting force_readonly before each load and clearing it
> when the load reads it:
>
> - needs_ro_update() now sets force_readonly whenever it returns true:
> to 1 for a DISK_RO=1 uevent, and to 0 when all of the map's paths
> are writable. uev_update_path() no longer sets or clears it itself.
> If the map has no dm info, needs_ro_update() now fetches it, and
> returns false if that fails, instead of assuming a reload is needed.
>
> - ev_add_path() sets it from all of the map's paths rather than only
> the path being added, and only when it is about to load the map
> (need_do_map). mpp->paths is up to date there after adopt_paths(),
> while mpp->pg doesn't contain the new paths yet.
>
> - update_map(), which does reloads that were delayed while the map was
> waiting for udev (UDEV_WAIT_RELOAD), recomputes it from the map's
> paths before setting up the map.
>
> - dm_addmap_create() and dm_addmap_reload() clear it as soon as they
> have read it, so it only applies to the load it was set for.
>
> - If a reload fails, dm_addmap_reload() sets it back, because the map
> still has its old table. If the map was supposed to become read-only,
> the next reload then tries again. needs_ro_update() clears the flag
> again when a DISK_RO=0 uevent arrives for a read-write map and none
> of the map's paths is read-only any more, so that a later reload for
> an unrelated reason, such as a path group change, doesn't load the
> map read-only.
>
> Signed-off-by: Brian Bunker <[email protected]>
> ---
> libmultipath/devmapper.c | 26 ++++++--
> multipathd/main.c | 128 +++++++++++++++++++++++++--------------
> 2 files changed, 103 insertions(+), 51 deletions(-)
>
> diff --git a/libmultipath/devmapper.c b/libmultipath/devmapper.c
> index e3870f59..324a92cc 100644
> --- a/libmultipath/devmapper.c
> +++ b/libmultipath/devmapper.c
> @@ -539,10 +539,15 @@ static uint16_t build_udev_flags(const struct multipath
> *mpp, int reload)
>
> int dm_addmap_create (struct multipath *mpp, char *params)
> {
> - int ro;
> + int ro = mpp->force_readonly ? 1 : 0;
> uint16_t udev_flags = build_udev_flags(mpp, 0);
>
> - for (ro = mpp->force_readonly ? 1 : 0; ro <= 1; ro++) {
> + /*
> + * force_readonly only applies to this load. Clear it, so that it
> + * can't affect later loads, even if this one fails.
> + */
> + mpp->force_readonly = 0;
> + for (; ro <= 1; ro++) {
> int err;
>
> if (dm_addmap(DM_DEVICE_CREATE, TGT_MPATH, mpp, params, ro,
> @@ -578,19 +583,26 @@ int dm_addmap_create (struct multipath *mpp, char
> *params)
> int dm_addmap_reload(struct multipath *mpp, char *params, int flush)
> {
> int r = 0;
> + int force_ro = mpp->force_readonly;
> uint16_t udev_flags = build_udev_flags(mpp, 1);
>
> + /*
> + * force_readonly only applies to this load. Clear it, so that it
> + * can't affect later loads, unless this one fails (see below).
> + */
> + mpp->force_readonly = 0;
> +
> /*
> * DM_DEVICE_RELOAD cannot wait on a cookie, as
> * the cookie will only ever be released after an
> * DM_DEVICE_RESUME. So call DM_DEVICE_RESUME
> * after each successful call to DM_DEVICE_RELOAD.
> */
> - if (!mpp->force_readonly)
> + if (!force_ro)
> r = dm_addmap(DM_DEVICE_RELOAD, TGT_MPATH, mpp, params,
> ADDMAP_RW, 0);
> if (!r) {
> - if (!mpp->force_readonly && errno != EROFS)
> + if (!force_ro && errno != EROFS)
> return 0;
> r = dm_addmap(DM_DEVICE_RELOAD, TGT_MPATH, mpp,
> params, ADDMAP_RO, 0);
> @@ -609,6 +621,12 @@ int dm_addmap_reload(struct multipath *mpp, char
> *params, int flush)
> dm_simplecmd(DM_DEVICE_RESUME, mpp->alias,
> DMFL_NEED_SYNC | (flush ? 0 : DMFL_NO_FLUSH),
> udev_flags);
> + /*
> + * The map still has its old table. If it was supposed to become
> + * read-only, keep force_readonly set, so that the next reload
> + * tries again.
> + */
> + mpp->force_readonly = force_ro;
> return 0;
Unsetting and then resetting force_readonly seems like more work than
necessary. It seems simpler to just clear mpp->force_readonly if we
successfully reload the table and resume the map.
> }
>
> diff --git a/multipathd/main.c b/multipathd/main.c
> index 9bce4d6b..ddef64fa 100644
> --- a/multipathd/main.c
> +++ b/multipathd/main.c
> @@ -709,6 +709,55 @@ void cleanup_reset_vec(struct vector_s **v)
> vector_reset(*v);
> }
>
> +static int
> +sysfs_get_ro (struct path *pp)
> +{
> + int ro;
> + char buff[3]; /* Either "0\n\0" or "1\n\0" */
> +
> + if (!pp->udev)
> + return -1;
> +
> + if (!sysfs_attr_get_value_ok(pp->udev, "ro", buff, sizeof(buff))) {
> + condlog(3, "%s: Cannot read ro attribute in sysfs", pp->dev);
> + return -1;
> + }
> +
> + if (sscanf(buff, "%d\n", &ro) != 1 || ro < 0 || ro > 1) {
> + condlog(3, "%s: Cannot parse ro attribute", pp->dev);
> + return -1;
> + }
> +
> + return ro;
> +}
> +
> +/* A map must be loaded read-only if any of its paths is read-only. */
> +static bool
> +has_ro_path(vector paths)
> +{
> + struct path *pp;
> + unsigned int i;
> +
> + vector_foreach_slot (paths, pp, i) {
> + if (sysfs_get_ro(pp) == 1)
> + return true;
> + }
> + return false;
> +}
> +
> +static bool
> +map_has_ro_path(struct multipath *mpp)
> +{
> + struct pathgroup *pgp;
> + unsigned int i;
> +
> + vector_foreach_slot (mpp->pg, pgp, i) {
> + if (has_ro_path(pgp->paths))
> + return true;
> + }
> + return false;
> +}
> +
> static int
> update_map (struct multipath *mpp, struct vectors *vecs, int new_map)
> {
> @@ -732,6 +781,14 @@ 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->paths is up to date
> + * after adopt_paths(), while mpp->pg isn't until setup_map().
> + */
> + mpp->force_readonly = has_ro_path(mpp->paths);
> +
> if (setup_map(mpp, ¶ms, vecs)) {
> condlog(0, "%s: failed to setup new map in update", mpp->alias);
> retries = -1;
> @@ -1270,28 +1327,6 @@ out:
> return ret;
> }
>
> -static int
> -sysfs_get_ro (struct path *pp)
> -{
> - int ro;
> - char buff[3]; /* Either "0\n\0" or "1\n\0" */
> -
> - if (!pp->udev)
> - return -1;
> -
> - if (!sysfs_attr_get_value_ok(pp->udev, "ro", buff, sizeof(buff))) {
> - condlog(3, "%s: Cannot read ro attribute in sysfs", pp->dev);
> - return -1;
> - }
> -
> - if (sscanf(buff, "%d\n", &ro) != 1 || ro < 0 || ro > 1) {
> - condlog(3, "%s: Cannot parse ro attribute", pp->dev);
> - return -1;
> - }
> -
> - return ro;
> -}
> -
> /*
> * returns:
> * 0: added
> @@ -1305,7 +1340,6 @@ 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;
>
> /*
> @@ -1370,14 +1404,16 @@ 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;
> -
> if (!need_do_map)
> return 0;
>
> + /*
> + * Load the map read-only if any of its paths is read-only, not
> + * just the one being added. mpp->paths is up to date after
> + * adopt_paths(), while mpp->pg doesn't have the new paths yet.
> + */
> + mpp->force_readonly = has_ro_path(mpp->paths);
> +
> if (!dm_map_present(mpp->alias)) {
> mpp->action = ACT_CREATE;
> start_waiter = 1;
> @@ -1596,24 +1632,26 @@ finish_path_init(struct path *pp, struct vectors *
> vecs)
> static bool
> needs_ro_update(struct multipath *mpp, int ro)
> {
> - struct pathgroup * pgp;
> - struct path * pp;
> - unsigned int i, j;
> -
> if (!mpp || ro < 0)
> return false;
I said we should clear mpp->force_reload when we return false, but we
obviously can't do that when mpp is NULL. Perhaps if ro is -1 in
uev_update_path(), we should check sysfs instead. Something like:
if (ro < 0)
ro = (sysfs_get_ro == 1);
That way we'd always call needs_ro_update() with a valid value for
ro.
> - if (!has_dm_info(mpp))
> - return true;
> - if (mpp->dmi.read_only == ro)
> + if (!has_dm_info(mpp) &&
> + dm_get_info(mpp->alias, &mpp->dmi) != DMP_OK) {
> + condlog(2, "%s: failed to get dm info", mpp->alias);
> return false;
Not sure it matters what we do here. I supposed that we could check all
the paths and set force_readonly if one of them is read-only.
> - if (ro == 1)
> - return true;
> - vector_foreach_slot (mpp->pg, pgp, i) {
> - vector_foreach_slot (pgp->paths, pp, j) {
> - if (sysfs_get_ro(pp) == 1)
> - return false;
> - }
> }
> + if (mpp->dmi.read_only == ro) {
> + /*
> + * A failed read-only reload leaves force_readonly set while
> + * the map is still read-write. Clear it once no path is
> + * read-only any more.
> + */
> + if (ro == 0 && mpp->force_readonly && !map_has_ro_path(mpp))
> + mpp->force_readonly = 0;
This is correct.
> + return false;
> + }
> + if (ro == 0 && map_has_ro_path(mpp))
If ro is 0 and not equal to mpp->dmi.read_only, then that means the
map is already read-only. We don't need force_readonly here, since
dm_addmap_reload() won't be able to reload the map read-write unless it
can actually re-open the devices read-write (the path devices in the
existing table must be opened read-only since the multipath device is
read-only, so dm can't simply reuse them for the new table that it's
loading).
-Ben
> + return false;
> + mpp->force_readonly = ro;
> return true;
> }
>
> @@ -1732,15 +1770,11 @@ 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;
> retval = reload_and_sync_map(mpp, vecs);
> if (retval == 2)
> condlog(2, "%s: map removed during
> reload", pp->dev);
> - else {
> - pp->mpp->force_readonly = 0;
> + else
> condlog(2, "%s: map %s reloaded (retval
> %d)", uev->kernel, mpp->alias, retval);
> - }
> }
> }
> if (auto_resize != AUTO_RESIZE_NEVER && mpp &&
> --
> 2.56.0
