[PATCH 3.16 148/346] block: fix bdi vs gendisk lifetime mismatch

[Ben Hutchings]

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@xxxxxxxxx>

commit df08c32ce3be5be138c1dbfcba203314a3a7cd6f upstream.

The name for a bdi of a gendisk is derived from the gendisk's devt.
However, since the gendisk is destroyed before the bdi it leaves a
window where a new gendisk could dynamically reuse the same devt while a
bdi with the same name is still live.  Arrange for the bdi to hold a
reference against its "owner" disk device while it is registered.
Otherwise we can hit sysfs duplicate name collisions like the following:

 WARNING: CPU: 10 PID: 2078 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x64/0x80
 sysfs: cannot create duplicate filename '/devices/virtual/bdi/259:1'

 Hardware name: HP ProLiant DL580 Gen8, BIOS P79 05/06/2015
  0000000000000286 0000000002c04ad5 ffff88006f24f970 ffffffff8134caec
  ffff88006f24f9c0 0000000000000000 ffff88006f24f9b0 ffffffff8108c351
  0000001f0000000c ffff88105d236000 ffff88105d1031e0 ffff8800357427f8
 Call Trace:
  [<ffffffff8134caec>] dump_stack+0x63/0x87
  [<ffffffff8108c351>] __warn+0xd1/0xf0
  [<ffffffff8108c3cf>] warn_slowpath_fmt+0x5f/0x80
  [<ffffffff812a0d34>] sysfs_warn_dup+0x64/0x80
  [<ffffffff812a0e1e>] sysfs_create_dir_ns+0x7e/0x90
  [<ffffffff8134faaa>] kobject_add_internal+0xaa/0x320
  [<ffffffff81358d4e>] ? vsnprintf+0x34e/0x4d0
  [<ffffffff8134ff55>] kobject_add+0x75/0xd0
  [<ffffffff816e66b2>] ? mutex_lock+0x12/0x2f
  [<ffffffff8148b0a5>] device_add+0x125/0x610
  [<ffffffff8148b788>] device_create_groups_vargs+0xd8/0x100
  [<ffffffff8148b7cc>] device_create_vargs+0x1c/0x20
  [<ffffffff811b775c>] bdi_register+0x8c/0x180
  [<ffffffff811b7877>] bdi_register_dev+0x27/0x30
  [<ffffffff813317f5>] add_disk+0x175/0x4a0

Reported-by: Yi Zhang <yizhan@xxxxxxxxxx>
Tested-by: Yi Zhang <yizhan@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Fixed up missing 0 return in bdi_register_owner().

Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -611,7 +611,7 @@ void add_disk(struct gendisk *disk)
 
 	/* Register BDI before referencing it from bdev */
 	bdi = &disk->queue->backing_dev_info;
-	bdi_register_dev(bdi, disk_devt(disk));
+	bdi_register_owner(bdi, disk_to_dev(disk));
 
 	blk_register_region(disk_devt(disk), disk->minors, NULL,
 			    exact_match, exact_lock, disk);
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -100,6 +100,7 @@ struct backing_dev_info {
 	struct list_head work_list;
 
 	struct device *dev;
+	struct device *owner;
 
 	struct timer_list laptop_mode_wb_timer;
 
@@ -116,6 +117,7 @@ __printf(3, 4)
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...);
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
+int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner);
 void bdi_unregister(struct backing_dev_info *bdi);
 int __must_check bdi_setup_and_register(struct backing_dev_info *, char *, unsigned int);
 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -350,6 +350,20 @@ int bdi_register_dev(struct backing_dev_
 }
 EXPORT_SYMBOL(bdi_register_dev);
 
+int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner)
+{
+	int rc;
+
+	rc = bdi_register(bdi, NULL, "%u:%u", MAJOR(owner->devt),
+			MINOR(owner->devt));
+	if (rc)
+		return rc;
+	bdi->owner = owner;
+	get_device(owner);
+	return 0;
+}
+EXPORT_SYMBOL(bdi_register_owner);
+
 /*
  * Remove bdi from the global list and shutdown any threads we have running
  */
@@ -418,6 +432,11 @@ void bdi_unregister(struct backing_dev_i
 
 		device_unregister(dev);
 	}
+
+	if (bdi->owner) {
+		put_device(bdi->owner);
+		bdi->owner = NULL;
+	}
 }
 EXPORT_SYMBOL(bdi_unregister);