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Commit 46224705 authored by Xiao Guangrong's avatar Xiao Guangrong Committed by Chris Mason
Browse files

Btrfs: drop unnecessary device lock 



Drop device_list_mutex for the reader side  on clone_fs_devices and
btrfs_rm_device pathes since the fs_info->volume_mutex can ensure the device
list is not updated

btrfs_close_extra_devices is the initialized path, we can not add or remove
device at this time, so we can simply drop the mutex safely, like other
initialized function does(add_missing_dev, __find_device, __btrfs_open_devices
...).

Signed-off-by: default avatarXiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 0c1daee0

fs/btrfs/volumes.c

+6 −7
Original line number Diff line number Diff line
@@ -406,7 +406,7 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig) 
	fs_devices->latest_trans = orig->latest_trans;

	memcpy(fs_devices->fsid, orig->fsid, sizeof(fs_devices->fsid));



	mutex_lock(&orig->device_list_mutex);

	/* We have held the volume lock, it is safe to get the devices. */

	list_for_each_entry(orig_dev, &orig->devices, dev_list) {

		device = kzalloc(sizeof(*device), GFP_NOFS);

		if (!device)
@@ -429,10 +429,8 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig) 
		device->fs_devices = fs_devices;

		fs_devices->num_devices++;

	}

	mutex_unlock(&orig->device_list_mutex);

	return fs_devices;

error:

	mutex_unlock(&orig->device_list_mutex);

	free_fs_devices(fs_devices);

	return ERR_PTR(-ENOMEM);

}
@@ -443,7 +441,7 @@ int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices) 


	mutex_lock(&uuid_mutex);

again:

	mutex_lock(&fs_devices->device_list_mutex);

	/* This is the initialized path, it is safe to release the devices. */

	list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {

		if (device->in_fs_metadata)

			continue;
@@ -463,7 +461,6 @@ again: 
		kfree(device->name);

		kfree(device);

	}

	mutex_unlock(&fs_devices->device_list_mutex);



	if (fs_devices->seed) {

		fs_devices = fs_devices->seed;
@@ -1242,14 +1239,16 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) 


		device = NULL;

		devices = &root->fs_info->fs_devices->devices;

		mutex_lock(&root->fs_info->fs_devices->device_list_mutex);

		/*

		 * It is safe to read the devices since the volume_mutex

		 * is held.

		 */

		list_for_each_entry(tmp, devices, dev_list) {

			if (tmp->in_fs_metadata && !tmp->bdev) {

				device = tmp;

				break;

			}

		}

		mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);

		bdev = NULL;

		bh = NULL;

		disk_super = NULL;