[PATCH v2 0/2] loop: fix two issues introduced by prior commit

[PATCH v2 0/2] loop: fix two issues introduced by prior commit

[Dongli Zhang]

This patch set fix two issues introduced by prior commit.


[PATCH v2 1/2] loop: do not print warn message if partition scan is successful

[PATCH v2 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 v2 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part()

[PATCH v2 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)


Dongli Zhang

[PATCH v2 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 v2 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>
---
Changed since v1:
  * move the setting of lo->lo_state to Lo_unbound after partscan has finished as well
    (suggested by Jan Kara)

 drivers/block/loop.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 7908673..a13f5dc 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1034,6 +1034,16 @@ loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
 	return err;
 }
 
+static void loop_disable_partscan(struct loop_device *lo)
+{
+	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);
+}
+
 static int __loop_clr_fd(struct loop_device *lo, bool release)
 {
 	struct file *filp = NULL;
@@ -1089,16 +1099,12 @@ 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 +1127,18 @@ 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 inside loop_disable_partscan()
+	 * 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.
+	 */
+	loop_disable_partscan(lo);
+
 	/*
 	 * Need not hold loop_ctl_mutex to fput backing file.
 	 * Calling fput holding loop_ctl_mutex triggers a circular
-- 
2.7.4

Re: [PATCH v2 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part()

[Jan Kara]

On Thu 21-02-19 23:33:43, Dongli Zhang wrote:
> 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>
> ---
> Changed since v1:
>   * move the setting of lo->lo_state to Lo_unbound after partscan has finished as well
>     (suggested by Jan Kara)
> 
>  drivers/block/loop.c | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)

Thanks the patch looks good! Just one nit below:

> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 7908673..a13f5dc 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1034,6 +1034,16 @@ loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
>  	return err;
>  }
>  
> +static void loop_disable_partscan(struct loop_device *lo)
> +{

I don't think there's any benefit in having this small function with a single
caller and furthermore with the subtle sideeffect that it changes lo_state.
So I'd just put the code inline in __loop_clr_fd(). With that you can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v2 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part()

[Dongli Zhang]

On 02/22/2019 07:47 PM, Jan Kara wrote:
> On Thu 21-02-19 23:33:43, Dongli Zhang wrote:
>> 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>
>> ---
>> Changed since v1:
>>   * move the setting of lo->lo_state to Lo_unbound after partscan has finished as well
>>     (suggested by Jan Kara)
>>
>>  drivers/block/loop.c | 26 ++++++++++++++++++++++----
>>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> Thanks the patch looks good! Just one nit below:
> 
>> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
>> index 7908673..a13f5dc 100644
>> --- a/drivers/block/loop.c
>> +++ b/drivers/block/loop.c
>> @@ -1034,6 +1034,16 @@ loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
>>  	return err;
>>  }
>>  
>> +static void loop_disable_partscan(struct loop_device *lo)
>> +{
> 
> I don't think there's any benefit in having this small function with a single
> caller and furthermore with the subtle sideeffect that it changes lo_state.
> So I'd just put the code inline in __loop_clr_fd(). With that you can add:
> 
> Reviewed-by: Jan Kara <jack@suse.cz>

Thank you very much!

I will send out v3 with the Reviewed-by and put the code inline in __loop_clr_fd().

Dongli Zhang

> 
> 								Honza
>