The patch titled
fs/block_dev.c: avoid dereferencing a 'request_queue' after last close
has been added to the -mm tree. Its filename is
fs-block_devc-avoid-dereferencing-a-request_queue-after-last-close.patch
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Subject: fs/block_dev.c: avoid dereferencing a 'request_queue' after last close
From: NeilBrown <neilb@xxxxxxx>
On the last close of an 'md' device which as been stopped, the device is
destroyed and in particular the request_queue is freed. The free is done
in a separate thread so it might happen a short time later.
__blkdev_put calls bdev_inode_switch_bdi *after* ->release has been
called.
Since commit f758eeabeb96f87 ("writeback: split inode_wb_list_lock into
bdi_writeback.list_lock") bdev_inode_switch_bdi() will dereference the 'old'
bdi, which lives inside a request_queue, to get a spin lock. This causes
the last close on an md device to sometime take a spin_lock which lives in
freed memory - which results in an oops.
So move the called to bdev_inode_switch_bdi before the call to ->release.
Signed-off-by: NeilBrown <neilb@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Reviewed-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Tested-by: Lin Ming <mlin@xxxxxxxxxxxxx>
Cc: Sitsofe Wheeler <sitsofe@xxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/block_dev.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff -puN fs/block_dev.c~fs-block_devc-avoid-dereferencing-a-request_queue-after-last-close fs/block_dev.c
--- a/fs/block_dev.c~fs-block_devc-avoid-dereferencing-a-request_queue-after-last-close
+++ a/fs/block_dev.c
@@ -1430,6 +1430,12 @@ static int __blkdev_put(struct block_dev
sync_blockdev(bdev);
kill_bdev(bdev);
}
+ if (!bdev->bd_openers)
+ /* ->release can cause the old bdi to disappear,
+ * so must switch it out first
+ */
+ bdev_inode_switch_bdi(bdev->bd_inode,
+ &default_backing_dev_info);
if (bdev->bd_contains == bdev) {
if (disk->fops->release)
ret = disk->fops->release(disk, mode);
@@ -1442,8 +1448,6 @@ static int __blkdev_put(struct block_dev
disk_put_part(bdev->bd_part);
bdev->bd_part = NULL;
bdev->bd_disk = NULL;
- bdev_inode_switch_bdi(bdev->bd_inode,
- &default_backing_dev_info);
if (bdev != bdev->bd_contains)
victim = bdev->bd_contains;
bdev->bd_contains = NULL;
_
Patches currently in -mm which might be from neilb@xxxxxxx are
origin.patch
linux-next.patch
fs-block_devc-avoid-dereferencing-a-request_queue-after-last-close.patch
cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc.patch
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