[2/2] block: loop: delete partitions after clearing & changing fd
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Message ID 20200707084552.3294693-3-ming.lei@redhat.com
State New
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Series
  • block: loop: delete partitions after clearing & changing fd
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Commit Message

Ming Lei July 7, 2020, 8:45 a.m. UTC
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(-)

Comments

Christoph Hellwig July 7, 2020, 5:53 p.m. UTC | #1
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.
Ming Lei July 8, 2020, 9:13 a.m. UTC | #2
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;
Ming Lei July 8, 2020, 9:52 a.m. UTC | #3
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

Patch
diff mbox series

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;
 }