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

[Jens Axboe <axboe@kernel.dk>]

On 10/19/26 5:31 PM, Cyril Brulebois wrote:
> Hi,
> 
> Daan De Meyer via B4 Relay <devnull+daan.amutable.com@kernel.org> (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@amutable.com>
>> ---
>> 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@amutable.com
> 
> 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.

They need a respin.

-- 
Jens Axboe