Patchwork [3.5.y.z,extended,stable] Patch "btrfs: use rcu_barrier() to wait for bdev puts at unmount" has been added to staging queue

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Submitter Luis Henriques
Date March 19, 2013, 12:22 p.m.
Message ID <1363695767-8141-1-git-send-email-luis.henriques@canonical.com>
Download mbox | patch
Permalink /patch/229037/
State New
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Comments

Luis Henriques - March 19, 2013, 12:22 p.m.
This is a note to let you know that I have just added a patch titled

    btrfs: use rcu_barrier() to wait for bdev puts at unmount

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

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

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

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From fb5e30677089e58d058977d56fc63afcd3a1d32b Mon Sep 17 00:00:00 2001
From: Eric Sandeen <sandeen@redhat.com>
Date: Sat, 9 Mar 2013 15:18:39 +0000
Subject: [PATCH] btrfs: use rcu_barrier() to wait for bdev puts at unmount

commit bc178622d40d87e75abc131007342429c9b03351 upstream.

Doing this would reliably fail with -EBUSY for me:

# mount /dev/sdb2 /mnt/scratch; umount /mnt/scratch; mkfs.btrfs -f /dev/sdb2
...
unable to open /dev/sdb2: Device or resource busy

because mkfs.btrfs tries to open the device O_EXCL, and somebody still has it.

Using systemtap to track bdev gets & puts shows a kworker thread doing a
blkdev put after mkfs attempts a get; this is left over from the unmount
path:

btrfs_close_devices
	__btrfs_close_devices
		call_rcu(&device->rcu, free_device);
			free_device
				INIT_WORK(&device->rcu_work, __free_device);
				schedule_work(&device->rcu_work);

so unmount might complete before __free_device fires & does its blkdev_put.

Adding an rcu_barrier() to btrfs_close_devices() causes unmount to wait
until all blkdev_put()s are done, and the device is truly free once
unmount completes.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Luis Henriques <luis.henriques@canonical.com>
---
 fs/btrfs/volumes.c | 6 ++++++
 1 file changed, 6 insertions(+)

--
1.8.1.2

Patch

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2208f0f..446896d 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -609,6 +609,12 @@  int btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 		__btrfs_close_devices(fs_devices);
 		free_fs_devices(fs_devices);
 	}
+	/*
+	 * Wait for rcu kworkers under __btrfs_close_devices
+	 * to finish all blkdev_puts so device is really
+	 * free when umount is done.
+	 */
+	rcu_barrier();
 	return ret;
 }