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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@vger.kernel.org > Signed-off-by: Daan De Meyer 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 [*] https://github.com/linux-blktests/blktests/pull/260