[3.19.y-ckt stable] Patch "scsi: Fix a bdi reregistration race" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    scsi: Fix a bdi reregistration race

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 72fb25f976fda3e1e0702a99413739c15601d39b Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bart.vanassche at sandisk.com>
Date: Fri, 18 Sep 2015 17:23:42 -0700
Subject: scsi: Fix a bdi reregistration race

commit bf2cf3baa20b0a6cd2d08707ef05dc0e992a8aa0 upstream.

Unregister and reregister BDI devices in the proper order. This patch
avoids that the following kernel warning can get triggered:

WARNING: CPU: 7 PID: 203 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x68/0x80()
sysfs: cannot create duplicate filename '/devices/virtual/bdi/8:32'
Workqueue: events_unbound async_run_entry_fn
Call Trace:
[<ffffffff814ff5a4>] dump_stack+0x4c/0x65
[<ffffffff810746ba>] warn_slowpath_common+0x8a/0xc0
[<ffffffff81074736>] warn_slowpath_fmt+0x46/0x50
[<ffffffff81237ca8>] sysfs_warn_dup+0x68/0x80
[<ffffffff81237d8e>] sysfs_create_dir_ns+0x7e/0x90
[<ffffffff81291f58>] kobject_add_internal+0xa8/0x320
[<ffffffff812923a0>] kobject_add+0x60/0xb0
[<ffffffff8138c937>] device_add+0x107/0x5e0
[<ffffffff8138d018>] device_create_groups_vargs+0xd8/0x100
[<ffffffff8138d05c>] device_create_vargs+0x1c/0x20
[<ffffffff8117f233>] bdi_register+0x63/0x2a0
[<ffffffff8117f497>] bdi_register_dev+0x27/0x30
[<ffffffff81281549>] add_disk+0x1a9/0x4e0
[<ffffffffa00c5739>] sd_probe_async+0x119/0x1d0 [sd_mod]
[<ffffffff8109a81a>] async_run_entry_fn+0x4a/0x140
[<ffffffff81091078>] process_one_work+0x1d8/0x7c0
[<ffffffff81091774>] worker_thread+0x114/0x460
[<ffffffff81097878>] kthread+0xf8/0x110
[<ffffffff8150801f>] ret_from_fork+0x3f/0x70

See also patch "block: destroy bdi before blockdev is unregistered"
(commit ID 6cd18e711dd8).

Signed-off-by: Bart Van Assche <bart.vanassche at sandisk.com>
Reviewed-by: Hannes Reinecke <hare at suse.de>
Signed-off-by: James Bottomley <JBottomley at Odin.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/scsi/scsi_sysfs.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index e71eb8e..f582cc1 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -1074,9 +1074,7 @@ void __scsi_remove_device(struct scsi_device *sdev)
 		bsg_unregister_queue(sdev->request_queue);
 		device_unregister(&sdev->sdev_dev);
 		transport_remove_device(dev);
-		device_del(dev);
-	} else
-		put_device(&sdev->sdev_dev);
+	}

 	/*
 	 * Stop accepting new requests and wait until all queuecommand() and
@@ -1087,6 +1085,16 @@ void __scsi_remove_device(struct scsi_device *sdev)
 	blk_cleanup_queue(sdev->request_queue);
 	cancel_work_sync(&sdev->requeue_work);

+	/*
+	 * Remove the device after blk_cleanup_queue() has been called such
+	 * a possible bdi_register() call with the same name occurs after
+	 * blk_cleanup_queue() has called bdi_destroy().
+	 */
+	if (sdev->is_visible)
+		device_del(dev);
+	else
+		put_device(&sdev->sdev_dev);
+
 	if (sdev->host->hostt->slave_destroy)
 		sdev->host->hostt->slave_destroy(sdev);
 	transport_destroy_device(dev);
--
1.9.1