[dm-devel] [PATCH v2 0/4] dm pr_ops fixes

[Mike Snitzer]

On Sun, Jul 17 2022 at  6:45P -0400,
Mike Christie <michael.christie at oracle.com> wrote:

> The following patches were made over Linus's tree and fix a couple bugs
> in the pr_ops code when a reservation type other than one of the All
> Registrants types is used. They were tested with the Windows failover
> cluster verification tests and libiscsi's PGR tests.
> 
> The current dm pr_ops code works well for All Registrants because any
> registered path is the reservation holder. Commands like reserve and
> release can go down any path and the behavior is the same. The problems
> these patches fix is when only one path is the holder as is the case
> for the other reservation types which is used by Window Failover Cluster
> and Linux Cluster (tools like pacemaker + scsi/multipath_fence agents).
> For example for Registrants Only the path that got the RESERVE command is
> the reservation holder. The RELEASE must be sent down that path to release
> the reservation.
> 
> With our current design we send down non-registration PR commands down
> whatever path we are currenly using, and then later PR commands end
> up on different paths. To continue the current design where dm's pr_ops
> are just passing through requests, and to avoid adding PR state to dm
> these patches modify pr_reserve/release to work similar to pr_register
> where we loop over all paths or at least loop over all paths until we
> find the path we are looking for.
> 
> v2:
> - Added info about testing.
> - Added patch for pr_preempt.

I picked this set up for 5.20 and staged in linux-next.

I tweaked the patch headers a bit while proof-reading and
understanding the scope of the changes.

I noticed that dm_pr_clear is the only remaining dm_pr_* method that
is using dm_{prepare,unprepare}_ioctl. I assume that'll be fine, but
the one gap it leaves is handling for the possibility that the DM
device is suspended.  Shouldn't dm_call_pr() be enhanced to check:
if (dm_suspended_md(md)) ?

Mike