Re: [PATCH v2 0/2] loop, nbd: drop partitions left behind by the GD_NEED_PART_SCAN removal

[Cyril Brulebois]

Hi,

Daan De Meyer via B4 Relay <devnull+daan.amutable.com@xxxxxxxxxx> (2026-08-24):
> Commit 267ec4d7223a ("loop: fix partition scan race between udev and
> loop_reread_partitions()") stopped disk_force_media_change() from setting
> GD_NEED_PART_SCAN. The caller audit in that commit only considered the bit
> as a request to rescan partitions, but it did more than that:
> bdev_disk_changed() drops every entry in disk->part_tbl before it consults
> disk_has_partscan(), and only the re-adding half is gated on partition
> scanning being enabled. The lazy scan on the next open was therefore also
> the only thing removing partitions from a device that has partitions but
> no partition scanning.
> 
> Loop devices without LO_FLAGS_PARTSCAN are exactly such devices, and they
> are not unusual. bdev_add_partition() only rejects GENHD_FL_NO_PART disks,
> so BLKPG_ADD_PARTITION works while GD_SUPPRESS_PART_SCAN is set, and
> parted, libfdisk and systemd all fall back to BLKPG when BLKRRPART fails
> with -EINVAL, which is what a loop device without LO_FLAGS_PARTSCAN
> returns.
> 
> Commit c4f4c0fc551c ("loop: remove manually added partitions on detach")
> fixed the detach path after this was reported as loop devices picking up
> partition devices from a previously built image:
> 
>   https://bugs.debian.org/1141434
> 
> These two patches fix the two remaining places that relied on the same
> lazy cleanup, LOOP_CHANGE_FD and NBD_CLEAR_SOCK.
> 
> Regression tests for both paths have been submitted to blktests:
> 
>   https://github.com/linux-blktests/blktests/pull/259
>   https://github.com/linux-blktests/blktests/pull/260
> 
> Signed-off-by: Daan De Meyer <daan@xxxxxxxxxxxx>
> ---
> Changes in v2:
> - Rewrap the comments added by both patches so they fit in 80 columns
>   (Christoph Hellwig).
> - No functional change, so the review and test tags from v1 were carried
>   over.
> - Link to v1: https://patch.msgid.link/20260806-b4-loop-nbd-stale-partitions-v1-0-67bb75a8d7be@xxxxxxxxxxxx

It would be nice if those fixes could get picked up eventually. They
received a few Reviewed-by and Tested-by already, and that v2 is only
about line wrapping anyway.


Cheers,
-- 
Cyril Brulebois (kibi@xxxxxxxxxx)            <https://debamax.com/>
D-I release manager -- Release team member -- Freelance Consultant

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