Re: [PATCH v6 1/1] multipathd: don't leave maps read-only after write protect is cleared

[Benjamin Marzinski <bmarzins@redhat.com>]

On Mon, Nov 02, 2026 at 04:31:50PM -0800, 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
> once the load has succeeded:
> 
> - uev_update_path() no longer takes the path's ro state from the
>   uevent's DISK_RO. The uevent only says that something changed. The
>   kernel updates the ro attribute before it sends the uevent, so sysfs
>   is current when the uevent is handled, while the uevent itself may
>   have been queued behind later changes. It just calls
>   needs_ro_update(), which reads the ro state of all of the map's paths
>   from sysfs.
> 
> - needs_ro_update() no longer takes an ro value. It sets
>   force_readonly from the ro state of the map's paths, and returns true
>   if that differs from the map's current state. If the map is already
>   read-only and has to stay so, it clears the flag and returns false,
>   since dm has to reopen the paths for any read-write reload anyway. If
>   the map has no dm info, it fetches it, and returns false if that
>   fails, instead of assuming a reload is needed. Since the flag is
>   recomputed on every call, a failed read-only reload is retried on the
>   next uevent without any special handling.
> 
> - 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() clears it as soon as it has read it. A failed
>   create leaves no map behind, and the next create computes the flag
>   again.
> 
> - dm_addmap_reload() clears it once the reload and resume have
>   succeeded. If the reload fails, the map keeps its old table, and the
>   flag stays set so that the next reload tries again.
> 
> Signed-off-by: Brian Bunker <brian@purestorage.com>
Thanks for dealing with all the revisions

Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>