loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part()

Commit 0da03cab87e6
("loop: Fix deadlock when calling blkdev_reread_part()") moves
blkdev_reread_part() out of the loop_ctl_mutex. However,
GENHD_FL_NO_PART_SCAN is set before __blkdev_reread_part(). As a result,
__blkdev_reread_part() will fail the check of GENHD_FL_NO_PART_SCAN and
will not rescan the loop device to delete all partitions.

Below are steps to reproduce the issue:

step1 # dd if=/dev/zero of=tmp.raw bs=1M count=100
step2 # losetup -P /dev/loop0 tmp.raw
step3 # parted /dev/loop0 mklabel gpt
step4 # parted -a none -s /dev/loop0 mkpart primary 64s 1
step5 # losetup -d /dev/loop0

Step5 will not be able to delete /dev/loop0p1 (introduced by step4) and
there is below kernel warning message:

[  464.414043] __loop_clr_fd: partition scan of loop0 failed (rc=-22)

This patch sets GENHD_FL_NO_PART_SCAN after blkdev_reread_part().

Fixes: 0da03cab87e6 ("loop: Fix deadlock when calling blkdev_reread_part()")
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index e25df5e..1e6edd5 100644 (file)
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1089,16 +1089,12 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
                kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
        }
        mapping_set_gfp_mask(filp->f_mapping, gfp);
-       lo->lo_state = Lo_unbound;
        /* This is safe: open() is still holding a reference. */
        module_put(THIS_MODULE);
        blk_mq_unfreeze_queue(lo->lo_queue);
 
        partscan = lo->lo_flags & LO_FLAGS_PARTSCAN && bdev;
        lo_number = lo->lo_number;
-       lo->lo_flags = 0;
-       if (!part_shift)
-               lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
        loop_unprepare_queue(lo);
 out_unlock:
        mutex_unlock(&loop_ctl_mutex);
@@ -1121,6 +1117,23 @@ out_unlock:
                /* Device is gone, no point in returning error */
                err = 0;
        }
+
+       /*
+        * lo->lo_state is set to Lo_unbound here after above partscan has
+        * finished.
+        *
+        * There cannot be anybody else entering __loop_clr_fd() as
+        * lo->lo_backing_file is already cleared and Lo_rundown state
+        * protects us from all the other places trying to change the 'lo'
+        * device.
+        */
+       mutex_lock(&loop_ctl_mutex);
+       lo->lo_flags = 0;
+       if (!part_shift)
+               lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
+       lo->lo_state = Lo_unbound;
+       mutex_unlock(&loop_ctl_mutex);
+
        /*
         * Need not hold loop_ctl_mutex to fput backing file.
         * Calling fput holding loop_ctl_mutex triggers a circular