[PATCH v3 0/2] loop: fix two issues introduced by prior commit

[PATCH v3 0/2] loop: fix two issues introduced by prior commit

[Dongli Zhang]

This patch set fix two issues introduced by prior commit.


[PATCH v3 1/2] loop: do not print warn message if partition scan is successful
[PATCH v3 1/2] fixes d57f3374ba48 ("loop: Move special partition reread
handling in loop_clr_fd()") to not always print warn message even when
partition scan is successful.


[PATCH v3 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part()
[PATCH v3 2/2] fixes 0da03cab87e6 ("loop: Fix deadlock when calling
blkdev_reread_part()") to not set GENHD_FL_NO_PART_SCAN before partition
scan when detaching loop device from the file.

Changed since v1:
  * move the setting of lo->lo_state to Lo_unbound after partscan has finished as well
    (suggested by Jan Kara)

Changed since v2:
  * Put the code inline in __loop_clr_fd() but not introduce new function
    (suggested by Jan Kara)


Dongli Zhang

[PATCH v3 1/2] loop: do not print warn message if partition scan is successful

[Dongli Zhang]

Do not print warn message when the partition scan returns 0.

Fixes: d57f3374ba48 ("loop: Move special partition reread handling in loop_clr_fd()")
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 drivers/block/loop.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index cf55389..7908673 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1115,8 +1115,9 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
 			err = __blkdev_reread_part(bdev);
 		else
 			err = blkdev_reread_part(bdev);
-		pr_warn("%s: partition scan of loop%d failed (rc=%d)\n",
-			__func__, lo_number, err);
+		if (err)
+			pr_warn("%s: partition scan of loop%d failed (rc=%d)\n",
+				__func__, lo_number, err);
 		/* Device is gone, no point in returning error */
 		err = 0;
 	}
-- 
2.7.4

[PATCH v3 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part()

[Dongli Zhang]

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>
---
Changed since v1:
  * move the setting of lo->lo_state to Lo_unbound after partscan has finished as well
    (suggested by Jan Kara)

Changed since v2:
  * Put the code inline in __loop_clr_fd() but not introduce new function
    (suggested by Jan Kara)

 drivers/block/loop.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 7908673..7ec3297 100644
--- 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 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
 		/* 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
-- 
2.7.4

Re: [PATCH v3 0/2] loop: fix two issues introduced by prior commit

[Jens Axboe]

On 2/22/19 7:10 AM, Dongli Zhang wrote:
> This patch set fix two issues introduced by prior commit.
> 
> 
> [PATCH v3 1/2] loop: do not print warn message if partition scan is successful
> [PATCH v3 1/2] fixes d57f3374ba48 ("loop: Move special partition reread
> handling in loop_clr_fd()") to not always print warn message even when
> partition scan is successful.
> 
> 
> [PATCH v3 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part()
> [PATCH v3 2/2] fixes 0da03cab87e6 ("loop: Fix deadlock when calling
> blkdev_reread_part()") to not set GENHD_FL_NO_PART_SCAN before partition
> scan when detaching loop device from the file.
> 
> Changed since v1:
>   * move the setting of lo->lo_state to Lo_unbound after partscan has finished as well
>     (suggested by Jan Kara)
> 
> Changed since v2:
>   * Put the code inline in __loop_clr_fd() but not introduce new function
>     (suggested by Jan Kara)

Applied, thanks.

-- 
Jens Axboe