[PATCH 0/2] block: loop: delete partitions after clearing & changing fd

[PATCH 0/2] block: loop: delete partitions after clearing & changing fd

[Ming Lei]

Hi,

The 1st patch cleans up __loop_clr_fd a bit.

The 2nd patch fixes one issue which may make ghost partitions even
though after fd is cleared or changed.


Ming Lei (2):
  block: loop: share code of reread partitions
  block: loop: delete partitions after clearing & changing fd

 drivers/block/loop.c | 36 ++++++++++++++++++++----------------
 1 file changed, 20 insertions(+), 16 deletions(-)

-- 
2.25.2

[PATCH 1/2] block: loop: share code of reread partitions

[Ming Lei]

loop_reread_partitions() has been there for rereading partitions, so
replace the open code in __loop_clr_fd() with loop_reread_partitions()
by passing 'locked' parameter.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/loop.c | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a943207705dd..0e08468b9ce0 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -650,13 +650,17 @@ static inline void loop_update_dio(struct loop_device *lo)
 }
 
 static void loop_reread_partitions(struct loop_device *lo,
-				   struct block_device *bdev)
+				   struct block_device *bdev, bool locked)
 {
 	int rc;
 
-	mutex_lock(&bdev->bd_mutex);
-	rc = bdev_disk_changed(bdev, false);
-	mutex_unlock(&bdev->bd_mutex);
+	if (locked) {
+		rc = bdev_disk_changed(bdev, false);
+	} else {
+		mutex_lock(&bdev->bd_mutex);
+		rc = bdev_disk_changed(bdev, false);
+		mutex_unlock(&bdev->bd_mutex);
+	}
 	if (rc)
 		pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
 			__func__, lo->lo_number, lo->lo_file_name, rc);
@@ -754,7 +758,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 	 */
 	fput(old_file);
 	if (partscan)
-		loop_reread_partitions(lo, bdev);
+		loop_reread_partitions(lo, bdev, false);
 	return 0;
 
 out_err:
@@ -1179,7 +1183,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 	bdgrab(bdev);
 	mutex_unlock(&loop_ctl_mutex);
 	if (partscan)
-		loop_reread_partitions(lo, bdev);
+		loop_reread_partitions(lo, bdev, false);
 	if (claimed_bdev)
 		bd_abort_claiming(bdev, claimed_bdev, loop_configure);
 	return 0;
@@ -1270,16 +1274,7 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
 		 * must be at least one and it can only become zero when the
 		 * current holder is released.
 		 */
-		if (!release)
-			mutex_lock(&bdev->bd_mutex);
-		err = bdev_disk_changed(bdev, false);
-		if (!release)
-			mutex_unlock(&bdev->bd_mutex);
-		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;
+		loop_reread_partitions(lo, bdev, release);
 	}
 
 	/*
@@ -1420,7 +1415,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 out_unlock:
 	mutex_unlock(&loop_ctl_mutex);
 	if (partscan)
-		loop_reread_partitions(lo, bdev);
+		loop_reread_partitions(lo, bdev, false);
 
 	return err;
 }
-- 
2.25.2

Re: [PATCH 1/2] block: loop: share code of reread partitions

[Christoph Hellwig]

On Tue, Jul 07, 2020 at 04:45:51PM +0800, Ming Lei wrote:
> loop_reread_partitions() has been there for rereading partitions, so
> replace the open code in __loop_clr_fd() with loop_reread_partitions()
> by passing 'locked' parameter.
> 
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/block/loop.c | 29 ++++++++++++-----------------
>  1 file changed, 12 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index a943207705dd..0e08468b9ce0 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -650,13 +650,17 @@ static inline void loop_update_dio(struct loop_device *lo)
>  }
>  
>  static void loop_reread_partitions(struct loop_device *lo,
> -				   struct block_device *bdev)
> +				   struct block_device *bdev, bool locked)
>  {
>  	int rc;
>  
> -	mutex_lock(&bdev->bd_mutex);
> -	rc = bdev_disk_changed(bdev, false);
> -	mutex_unlock(&bdev->bd_mutex);
> +	if (locked) {
> +		rc = bdev_disk_changed(bdev, false);
> +	} else {
> +		mutex_lock(&bdev->bd_mutex);
> +		rc = bdev_disk_changed(bdev, false);
> +		mutex_unlock(&bdev->bd_mutex);
> +	}

functions with an argument based locking context are a really bad
idea.  And there is absolutely no reason to add them just for
a shared printk.

[PATCH 2/2] block: loop: delete partitions after clearing & changing fd

[Ming Lei]

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.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/loop.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 0e08468b9ce0..cf71a1bbcd45 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -650,17 +650,26 @@ static inline void loop_update_dio(struct loop_device *lo)
 }
 
 static void loop_reread_partitions(struct loop_device *lo,
-				   struct block_device *bdev, bool locked)
+				   struct block_device *bdev, bool locked,
+				   bool force_scan)
 {
 	int rc;
+	bool no_scan;
 
-	if (locked) {
-		rc = bdev_disk_changed(bdev, false);
-	} else {
+	if (!locked)
 		mutex_lock(&bdev->bd_mutex);
-		rc = bdev_disk_changed(bdev, false);
+
+	no_scan = lo->lo_disk->flags & GENHD_FL_NO_PART_SCAN;
+	if (force_scan && no_scan)
+		lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
+
+	rc = bdev_disk_changed(bdev, false);
+
+	if (force_scan && no_scan)
+		lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
+
+	if (!locked)
 		mutex_unlock(&bdev->bd_mutex);
-	}
 	if (rc)
 		pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
 			__func__, lo->lo_number, lo->lo_file_name, rc);
@@ -758,7 +767,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 	 */
 	fput(old_file);
 	if (partscan)
-		loop_reread_partitions(lo, bdev, false);
+		loop_reread_partitions(lo, bdev, false, true);
 	return 0;
 
 out_err:
@@ -1183,7 +1192,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 	bdgrab(bdev);
 	mutex_unlock(&loop_ctl_mutex);
 	if (partscan)
-		loop_reread_partitions(lo, bdev, false);
+		loop_reread_partitions(lo, bdev, false, false);
 	if (claimed_bdev)
 		bd_abort_claiming(bdev, claimed_bdev, loop_configure);
 	return 0;
@@ -1274,7 +1283,7 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
 		 * must be at least one and it can only become zero when the
 		 * current holder is released.
 		 */
-		loop_reread_partitions(lo, bdev, release);
+		loop_reread_partitions(lo, bdev, release, true);
 	}
 
 	/*
@@ -1415,7 +1424,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 out_unlock:
 	mutex_unlock(&loop_ctl_mutex);
 	if (partscan)
-		loop_reread_partitions(lo, bdev, false);
+		loop_reread_partitions(lo, bdev, false, false);
 
 	return err;
 }
-- 
2.25.2

Re: [PATCH 2/2] block: loop: delete partitions after clearing & changing fd

[Christoph Hellwig]

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.

Re: [PATCH 2/2] block: loop: delete partitions after clearing & changing fd

[Ming Lei]

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@redhat.com>
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.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/partitions/core.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/block/partitions/core.c b/block/partitions/core.c
index 78951e33b2d7..e62a98a8eeb7 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -619,8 +619,6 @@ int blk_drop_partitions(struct block_device *bdev)
 	struct disk_part_iter piter;
 	struct hd_struct *part;
 
-	if (!disk_part_scan_enabled(bdev->bd_disk))
-		return 0;
 	if (bdev->bd_part_count)
 		return -EBUSY;
 
-- 
2.25.2




thanks,
Ming

Re: [PATCH 2/2] block: loop: delete partitions after clearing & changing fd

[Ming Lei]

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@redhat.com>
> 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