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loop: remove manually added partitions on detach

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Commit 267ec4d722 ("loop: fix partition scan race between udev and
loop_reread_partitions()") stopped disk_force_media_change() from
setting GD_NEED_PART_SCAN because loop devices with LO_FLAGS_PARTSCAN
rescan partitions explicitly. However, partitions can also be added
manually with BLKPG while LO_FLAGS_PARTSCAN is clear.

When such a loop device is detached, __loop_clr_fd() skips
bdev_disk_changed(). Without GD_NEED_PART_SCAN, reopening the unbound
device no longer performs the previous lazy cleanup, leaving dead
partition devices behind. A subsequent LOOP_CONFIGURE can then fail its
partition scan with -EBUSY, as seen in blktests loop/009 after loop/008.

Call bdev_disk_changed() unconditionally during __loop_clr_fd(). The
disk capacity is already zero and the release path holds open_mutex, so
this drops all partitions without rescanning the detached backing file.

The new blktests loop/013 case covers this sequence by adding a partition
with BLKPG without LO_FLAGS_PARTSCAN, detaching the loop device, and
checking that the partition is gone when the device is reopened.

Fixes: 267ec4d722 ("loop: fix partition scan race between udev and loop_reread_partitions()")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202607150754.b660f5b9-lkp@intel.com
Signed-off-by: Daan De Meyer <daan@amutable.com>
Link: https://patch.msgid.link/20260715-b4-loop-partition-cleanup-v1-1-b9f59910cd1e@amutable.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Daan De Meyer
2026-07-15 21:39:57 +02:00
committed by Jens Axboe
parent 691b052139
commit c4f4c0fc55
1 changed files with 14 additions and 18 deletions
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32
drivers/block/loop.c
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@@ -1113,6 +1113,7 @@ static void __loop_clr_fd(struct loop_device *lo)
struct queue_limits lim;
struct file *filp;
gfp_t gfp = lo->old_gfp_mask;
int err;
spin_lock_irq(&lo->lo_lock);
filp = lo->lo_backing_file;
@@ -1146,26 +1147,21 @@ static void __loop_clr_fd(struct loop_device *lo)
disk_force_media_change(lo->lo_disk);
if (lo->lo_flags & LO_FLAGS_PARTSCAN) {
int err;
/*
* open_mutex has been held already in release path, so don't
* acquire it if this function is called in such case.
*
* If the reread partition isn't from release path, lo_refcnt
* must be at least one and it can only become zero when the
* current holder is released.
*/
err = bdev_disk_changed(lo->lo_disk, false);
if (err)
pr_warn("%s: partition scan of loop%d failed (rc=%d)\n",
__func__, lo->lo_number, err);
/* Device is gone, no point in returning error */
}
/*
* Remove all partitions, including partitions added manually with
* BLKPG, which may exist even if LO_FLAGS_PARTSCAN is not set.
*
* open_mutex has been held already in release path, so don't acquire
* it here.
*/
err = bdev_disk_changed(lo->lo_disk, false);
if (err)
pr_warn("%s: partition scan of loop%d failed (rc=%d)\n",
__func__, lo->lo_number, err);
/* Device is gone, no point in returning error */
/*
* lo->lo_state is set to Lo_unbound here after above partscan has
* lo->lo_state is set to Lo_unbound here after removing partitions has
* finished. There cannot be anybody else entering __loop_clr_fd() as
* Lo_rundown state protects us from all the other places trying to
* change the 'lo' device.