APPLIED: [PATCH][COSMIC-unstable] UBUNTU: SAUCE: (noup) zfs to 0.7.9-3ubuntu4

[Seth Forshee]

On Thu, Jul 12, 2018 at 12:03:14PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1781364
> 
> This is a sync of zfs 0.7.9-3ubuntu4 that fixes a mount/umount deadlock
> for upstream ZFS commit ac09630d8b0b ("Fix zpl_mount() deadlock")
> 
> ZFS commit 93b43af inadvertently introduced the following scenario which
> can result in a deadlock.  This issue was most easily reproduced by
> LXD containers using a ZFS storage backend but should be reproducible
> under any workload which is frequently mounting and unmounting.
> 
> -- THREAD A --
> spa_sync()
>   spa_sync_upgrades()
>     rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG); <- Waiting on B
> 
> -- THREAD B --
> mount_fs()
>   zpl_mount()
>     zpl_mount_impl()
>       dmu_objset_hold()
>         dmu_objset_hold_flags()
>           dsl_pool_hold()
>             dsl_pool_config_enter()
>               rrw_enter(&dp->dp_config_rwlock, RW_READER, tag);
>     sget()
>       sget_userns()
>         grab_super()
>           down_write(&s->s_umount); <- Waiting on C
> 
> -- THREAD C --
> cleanup_mnt()
>   deactivate_super()
>     down_write(&s->s_umount);
>     deactivate_locked_super()
>       zpl_kill_sb()
>         kill_anon_super()
>           generic_shutdown_super()
>             sync_filesystem()
>               zpl_sync_fs()
>                 zfs_sync()
>                   zil_commit()
>                     txg_wait_synced() <- Waiting on A
> 
> Signed-off-by: Brian Behlendorf <behlendorf1 at llnl.gov>
> (backport from ZFS upstream commit ac09630d8b0bf6c92084a30fdaefd03fd0adbdc1)
> Signed-off-by: Colin Ian King <colin.king at canonical.com>

Applied to cosmic/master-next and unstable/master, thanks!