block, loop: support partitions without scanning

Closes: #1012298

2 files changed, 94 insertions, 0 deletions

diff --git a/debian/patches/bugfix/all/block-loop-support-partitions-without-scanning.patch b/debian/patches/bugfix/all/block-loop-support-partitions-without-scanning.patch
new file mode 100644
index 000000000..99861bda7
--- /dev/null
+++ b/debian/patches/bugfix/all/block-loop-support-partitions-without-scanning.patch
@@ -0,0 +1,93 @@
+From: Christoph Hellwig <hch@lst.de>
+Date: Fri, 27 May 2022 07:58:06 +0200
+Subject: block, loop: support partitions without scanning
+Origin: https://git.kernel.org/linus/b9684a71fca793213378dd410cd11675d973eaa1
+Bug-Debian: https://bugs.debian.org/1012298
+
+Historically we did distinguish between a flag that surpressed partition
+scanning, and a combinations of the minors variable and another flag if
+any partitions were supported.  This was generally confusing and doesn't
+make much sense, but some corner case uses of the loop driver actually
+do want to support manually added partitions on a device that does not
+actively scan for partitions.  To make things worsee the loop driver
+also wants to dynamically toggle the scanning for partitions on a live
+gendisk, which makes the disk->flags updates non-atomic.
+
+Introduce a new GD_SUPPRESS_PART_SCAN bit in disk->state that disables
+just scanning for partitions, and toggle that instead of GENHD_FL_NO_PART
+in the loop driver.
+
+Fixes: 1ebe2e5f9d68 ("block: remove GENHD_FL_EXT_DEVT")
+Reported-by: Ming Lei <ming.lei@redhat.com>
+Signed-off-by: Christoph Hellwig <hch@lst.de>
+Reviewed-by: Ming Lei <ming.lei@redhat.com>
+Link: https://lore.kernel.org/r/20220527055806.1972352-1-hch@lst.de
+Signed-off-by: Jens Axboe <axboe@kernel.dk>
+[Backport to 5.18.y: Refresh context in drivers/block/loop.c not containing
+a0e286b6a5b6 ("loop: remove lo_refcount and avoid lo_mutex in ->open /
+->release")]
+---
+ block/genhd.c          | 2 ++
+ drivers/block/loop.c   | 8 ++++----
+ include/linux/blkdev.h | 1 +
+ 3 files changed, 7 insertions(+), 4 deletions(-)
+
+--- a/block/genhd.c
++++ b/block/genhd.c
+@@ -385,6 +385,8 @@ int disk_scan_partitions(struct gendisk
+ 
+ 	if (disk->flags & (GENHD_FL_NO_PART | GENHD_FL_HIDDEN))
+ 		return -EINVAL;
++	if (test_bit(GD_SUPPRESS_PART_SCAN, &disk->state))
++		return -EINVAL;
+ 	if (disk->open_partitions)
+ 		return -EBUSY;
+ 
+--- a/drivers/block/loop.c
++++ b/drivers/block/loop.c
+@@ -1066,7 +1066,7 @@ static int loop_configure(struct loop_de
+ 		lo->lo_flags |= LO_FLAGS_PARTSCAN;
+ 	partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
+ 	if (partscan)
+-		lo->lo_disk->flags &= ~GENHD_FL_NO_PART;
++		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
+ 
+ 	loop_global_unlock(lo, is_loop);
+ 	if (partscan)
+@@ -1185,7 +1185,7 @@ static void __loop_clr_fd(struct loop_de
+ 	 */
+ 	lo->lo_flags = 0;
+ 	if (!part_shift)
+-		lo->lo_disk->flags |= GENHD_FL_NO_PART;
++		set_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
+ 	mutex_lock(&lo->lo_mutex);
+ 	lo->lo_state = Lo_unbound;
+ 	mutex_unlock(&lo->lo_mutex);
+@@ -1295,7 +1295,7 @@ out_unfreeze:
+ 
+ 	if (!err && (lo->lo_flags & LO_FLAGS_PARTSCAN) &&
+ 	     !(prev_lo_flags & LO_FLAGS_PARTSCAN)) {
+-		lo->lo_disk->flags &= ~GENHD_FL_NO_PART;
++		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
+ 		partscan = true;
+ 	}
+ out_unlock:
+@@ -2045,7 +2045,7 @@ static int loop_add(int i)
+ 	 * userspace tools. Parameters like this in general should be avoided.
+ 	 */
+ 	if (!part_shift)
+-		disk->flags |= GENHD_FL_NO_PART;
++		set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
+ 	atomic_set(&lo->lo_refcnt, 0);
+ 	mutex_init(&lo->lo_mutex);
+ 	lo->lo_number		= i;
+--- a/include/linux/blkdev.h
++++ b/include/linux/blkdev.h
+@@ -147,6 +147,7 @@ struct gendisk {
+ #define GD_DEAD				2
+ #define GD_NATIVE_CAPACITY		3
+ #define GD_ADDED			4
++#define GD_SUPPRESS_PART_SCAN		5
+ 
+ 	struct mutex open_mutex;	/* open/close mutex */
+ 	unsigned open_partitions;	/* number of open partitions */
diff --git a/debian/patches/series b/debian/patches/series
index 5b446fb2f..b0da24cfe 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -81,6 +81,7 @@ features/x86/x86-make-x32-syscall-support-conditional.patch
 bugfix/all/disable-some-marvell-phys.patch
 bugfix/all/fs-add-module_softdep-declarations-for-hard-coded-cr.patch
 bugfix/all/sign-file-Convert-API-usage-to-support-OpenSSL-v3.patch
+bugfix/all/block-loop-support-partitions-without-scanning.patch
 
 # Miscellaneous features