On Wed, Jul 08, 2020 at 05:13:18PM +0800, Ming Lei wrote: > On Tue, Jul 07, 2020 at 07:53:12PM +0200, Christoph Hellwig wrote: > > On Tue, Jul 07, 2020 at 04:45:52PM +0800, Ming Lei wrote: > > > After clearing fd or changing fd, we have to delete old partitions, > > > otherwise they may become ghost partitions. > > > > > > Fix this issue by clearing GENHD_FL_NO_PART_SCAN during calling > > > bdev_disk_changed() which won't drop old partitions if GENHD_FL_NO_PART_SCAN > > > isn't set. > > > > I don't think messing with GENHD_FL_NO_PART_SCAN is a good idea, as > > that will also cause an actual partition scan. But except for historic > > reasons I can't think of a good idea to even check for > > GENHD_FL_NO_PART_SCAN in blk_drop_partitions. > > I think it is safe to not check it in blk_drop_partitions(), how about > the following patch? > > From a20209464c367c338beee5555f2cb5c8e8ad9f78 Mon Sep 17 00:00:00 2001 > From: Ming Lei <ming.lei@xxxxxxxxxx> > Date: Wed, 8 Jul 2020 16:07:19 +0800 > Subject: [PATCH] block: always remove partitions in blk_drop_partitions() > > So far blk_drop_partitions() only removes partitions when > disk_part_scan_enabled() return true. This way can make ghost partition on > loop device after changing/clearing FD in case that PARTSCAN is disabled. > > Fix this issue by always removing partitions in blk_drop_partitions(), and > this way is correct because: > > 1) only loop, mmc and GENHD_FL_HIDDEN disks(nvme multipath) may set > GENHD_FL_NO_PART_SCAN > > 2) GENHD_FL_HIDDEN disks doesn't expose disk to block device fs, and > bdev_disk_changed()/blk_drop_partitions() won't be called for this kind of > disk > > 3) for mmc, if GENHD_FL_NO_PART_SCAN is set, no any partitions can be added > for this kind of disk, so blk_drop_partitions() basically does nothing no > matter if GENHD_FL_NO_PART_SCAN is set or not because disk_max_parts(disk) <= 1 > > 4) for loop, bdev_disk_changed() is called in two cases: one is set fd and set > status, when there shouldn't be any partitions; another is clearing/changing fd, > we need to remove old partitions and re-read new partitions if there are and > PART_SCAN is enabled. BTW, the partitions shouldn't have been added, but ioctl(BLKPG, BLKPG_ADD_PARTITION) doesn't check GENHD_FL_NO_PART_SCAN, so the partitions are added. However, changing ioctl(BLKPG, BLKPG_ADD_PARTITION) might break some userspace. Thanks, Ming
