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Btrfs: drop unnecessary device lock

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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: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Xiao Guangrong 2011-04-20 10:08:47 +00:00 committed by Chris Mason
parent 0c1daee085
commit 4622470565
1 changed files with 6 additions and 7 deletions
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13
fs/btrfs/volumes.c
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@ -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;