[PATCH 4.9 133/141] btrfs: iterate all devices during trim, instead of fs_devices::alloc_list

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Jeff Mahoney <jeffm@xxxxxxxx>

commit d4e329de5e5e21594df2e0dd59da9acee71f133b upstream.

btrfs_trim_fs iterates over the fs_devices->alloc_list while holding the
device_list_mutex.  The problem is that ->alloc_list is protected by the
chunk mutex.  We don't want to hold the chunk mutex over the trim of the
entire file system.  Fortunately, the ->dev_list list is protected by
the dev_list mutex and while it will give us all devices, including
read-only devices, we already just skip the read-only devices.  Then we
can continue to take and release the chunk mutex while scanning each
device.

Fixes: 499f377f49f ("btrfs: iterate over unused chunk space in FITRIM")
CC: stable@xxxxxxxxxxxxxxx # 4.4+
Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/btrfs/extent-tree.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -11193,8 +11193,8 @@ int btrfs_trim_fs(struct btrfs_root *roo
 	}
 
 	mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
-	devices = &root->fs_info->fs_devices->alloc_list;
-	list_for_each_entry(device, devices, dev_alloc_list) {
+	devices = &root->fs_info->fs_devices->devices;
+	list_for_each_entry(device, devices, dev_list) {
 		ret = btrfs_trim_free_extents(device, range->minlen,
 					      &group_trimmed);
 		if (ret)