block: fix bdi vs gendisk lifetime mismatch

djbw · axboe · commit df08c32ce3be · 2016-08-04T14:19:16.000-06:00
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:
  [&lt;ffffffff8134caec&gt;] dump_stack+0x63/0x87
  [&lt;ffffffff8108c351&gt;] __warn+0xd1/0xf0
  [&lt;ffffffff8108c3cf&gt;] warn_slowpath_fmt+0x5f/0x80
  [&lt;ffffffff812a0d34&gt;] sysfs_warn_dup+0x64/0x80
  [&lt;ffffffff812a0e1e&gt;] sysfs_create_dir_ns+0x7e/0x90
  [&lt;ffffffff8134faaa&gt;] kobject_add_internal+0xaa/0x320
  [&lt;ffffffff81358d4e&gt;] ? vsnprintf+0x34e/0x4d0
  [&lt;ffffffff8134ff55&gt;] kobject_add+0x75/0xd0
  [&lt;ffffffff816e66b2&gt;] ? mutex_lock+0x12/0x2f
  [&lt;ffffffff8148b0a5&gt;] device_add+0x125/0x610
  [&lt;ffffffff8148b788&gt;] device_create_groups_vargs+0xd8/0x100
  [&lt;ffffffff8148b7cc&gt;] device_create_vargs+0x1c/0x20
  [&lt;ffffffff811b775c&gt;] bdi_register+0x8c/0x180
  [&lt;ffffffff811b7877&gt;] bdi_register_dev+0x27/0x30
  [&lt;ffffffff813317f5&gt;] add_disk+0x175/0x4a0

Cc: &lt;stable@vger.kernel.org&gt;
Reported-by: Yi Zhang &lt;yizhan@redhat.com&gt;
Tested-by: Yi Zhang &lt;yizhan@redhat.com&gt;
Signed-off-by: Dan Williams &lt;dan.j.williams@intel.com&gt;

Fixed up missing 0 return in bdi_register_owner().

Signed-off-by: Jens Axboe &lt;axboe@fb.com&gt;
diff --git a/block/genhd.c b/block/genhd.c
@@ -614,7 +614,7 @@ void device_add_disk(struct device *parent, 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);
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
@@ -163,6 +163,7 @@ struct backing_dev_info {
 	wait_queue_head_t wb_waitq;
 
 	struct device *dev;
+	struct device *owner;
 
 	struct timer_list laptop_mode_wb_timer;
 
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
@@ -24,6 +24,7 @@ __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 *);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
@@ -825,6 +825,20 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t 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 bdi_list, and ensure that it is no longer visible
  */
@@ -849,6 +863,11 @@ void bdi_unregister(struct backing_dev_info *bdi)
 		device_unregister(bdi->dev);
 		bdi->dev = NULL;
 	}
+
+	if (bdi->owner) {
+		put_device(bdi->owner);
+		bdi->owner = NULL;
+	}
 }
 
 void bdi_exit(struct backing_dev_info *bdi)
