Re: [PATCH 2/2] nbd: drop stale partitions on NBD_CLEAR_SOCK

[Shin'ichiro Kawasaki]

On Aug 06, 2026 / 12:36, Daan De Meyer via B4 Relay wrote:
> From: Daan De Meyer <daan@xxxxxxxxxxxx>
> 
> Commit 267ec4d7223a ("loop: fix partition scan race between udev and
> loop_reread_partitions()") stopped disk_force_media_change() from
> setting GD_NEED_PART_SCAN. Besides requesting a rescan, that bit was what
> removed stale partitions on the next open, as bdev_disk_changed() drops
> all partitions before it consults disk_has_partscan().
> 
> nbd_clear_sock_ioctl() relied on that. It zeroes the capacity through
> nbd_bdev_reset(), but nothing removes the partitions of the disconnected
> device anymore. With the default max_part=16 they linger until the next
> connect sets GD_NEED_PART_SCAN again. With max_part=0 nothing ever sets
> it, so they are never removed at all, even though nbd does not set
> GENHD_FL_NO_PART and partitions can therefore still be added with BLKPG.
> 
> Set GD_NEED_PART_SCAN in nbd_clear_sock_ioctl() so the partitions are
> dropped on the next open. Calling bdev_disk_changed() directly is not an
> option as it needs open_mutex, which nbd_open() acquires under
> config_lock.
> 
> Fixes: 267ec4d7223a ("loop: fix partition scan race between udev and loop_reread_partitions()")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Daan De Meyer <daan@xxxxxxxxxxxx>

Daan provided another new, blktests test case to recreate the problem describe
above [*]. I confirmed that the test case failed on v7.2-rc7 kernel, and this
patch avoids the failure.

Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>

[*] https://github.com/linux-blktests/blktests/pull/260