Btrfs: using rcu lock in the reader side of devices list
fs_devices->devices is only updated on remove and add device paths, so we can
use rcu to protect it in the reader side
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 0b5ca27..e7844f8 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -363,7 +363,7 @@
INIT_LIST_HEAD(&device->dev_alloc_list);
mutex_lock(&fs_devices->device_list_mutex);
- list_add(&device->dev_list, &fs_devices->devices);
+ list_add_rcu(&device->dev_list, &fs_devices->devices);
mutex_unlock(&fs_devices->device_list_mutex);
device->fs_devices = fs_devices;
@@ -471,6 +471,29 @@
return 0;
}
+static void __free_device(struct work_struct *work)
+{
+ struct btrfs_device *device;
+
+ device = container_of(work, struct btrfs_device, rcu_work);
+
+ if (device->bdev)
+ blkdev_put(device->bdev, device->mode);
+
+ kfree(device->name);
+ kfree(device);
+}
+
+static void free_device(struct rcu_head *head)
+{
+ struct btrfs_device *device;
+
+ device = container_of(head, struct btrfs_device, rcu);
+
+ INIT_WORK(&device->rcu_work, __free_device);
+ schedule_work(&device->rcu_work);
+}
+
static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
{
struct btrfs_device *device;
@@ -480,18 +503,27 @@
mutex_lock(&fs_devices->device_list_mutex);
list_for_each_entry(device, &fs_devices->devices, dev_list) {
- if (device->bdev) {
- blkdev_put(device->bdev, device->mode);
+ struct btrfs_device *new_device;
+
+ if (device->bdev)
fs_devices->open_devices--;
- }
+
if (device->writeable) {
list_del_init(&device->dev_alloc_list);
fs_devices->rw_devices--;
}
- device->bdev = NULL;
- device->writeable = 0;
- device->in_fs_metadata = 0;
+ new_device = kmalloc(sizeof(*new_device), GFP_NOFS);
+ BUG_ON(!new_device);
+ memcpy(new_device, device, sizeof(*new_device));
+ new_device->name = kstrdup(device->name, GFP_NOFS);
+ BUG_ON(!new_device->name);
+ new_device->bdev = NULL;
+ new_device->writeable = 0;
+ new_device->in_fs_metadata = 0;
+ list_replace_rcu(&device->dev_list, &new_device->dev_list);
+
+ call_rcu(&device->rcu, free_device);
}
mutex_unlock(&fs_devices->device_list_mutex);
@@ -1204,11 +1236,13 @@
struct block_device *bdev;
struct buffer_head *bh = NULL;
struct btrfs_super_block *disk_super;
+ struct btrfs_fs_devices *cur_devices;
u64 all_avail;
u64 devid;
u64 num_devices;
u8 *dev_uuid;
int ret = 0;
+ bool clear_super = false;
mutex_lock(&uuid_mutex);
mutex_lock(&root->fs_info->volume_mutex);
@@ -1294,6 +1328,7 @@
list_del_init(&device->dev_alloc_list);
unlock_chunks(root);
root->fs_info->fs_devices->rw_devices--;
+ clear_super = true;
}
ret = btrfs_shrink_device(device, 0);
@@ -1304,16 +1339,15 @@
if (ret)
goto error_undo;
- device->in_fs_metadata = 0;
-
/*
* the device list mutex makes sure that we don't change
* the device list while someone else is writing out all
* the device supers.
*/
+
+ cur_devices = device->fs_devices;
mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
- list_del_init(&device->dev_list);
- mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
+ list_del_rcu(&device->dev_list);
device->fs_devices->num_devices--;
@@ -1327,36 +1361,36 @@
if (device->bdev == root->fs_info->fs_devices->latest_bdev)
root->fs_info->fs_devices->latest_bdev = next_device->bdev;
- if (device->bdev) {
- blkdev_put(device->bdev, device->mode);
- device->bdev = NULL;
+ if (device->bdev)
device->fs_devices->open_devices--;
- }
+
+ call_rcu(&device->rcu, free_device);
+ mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
num_devices = btrfs_super_num_devices(&root->fs_info->super_copy) - 1;
btrfs_set_super_num_devices(&root->fs_info->super_copy, num_devices);
- if (device->fs_devices->open_devices == 0) {
+ if (cur_devices->open_devices == 0) {
struct btrfs_fs_devices *fs_devices;
fs_devices = root->fs_info->fs_devices;
while (fs_devices) {
- if (fs_devices->seed == device->fs_devices)
+ if (fs_devices->seed == cur_devices)
break;
fs_devices = fs_devices->seed;
}
- fs_devices->seed = device->fs_devices->seed;
- device->fs_devices->seed = NULL;
+ fs_devices->seed = cur_devices->seed;
+ cur_devices->seed = NULL;
lock_chunks(root);
- __btrfs_close_devices(device->fs_devices);
+ __btrfs_close_devices(cur_devices);
unlock_chunks(root);
- free_fs_devices(device->fs_devices);
+ free_fs_devices(cur_devices);
}
/*
* at this point, the device is zero sized. We want to
* remove it from the devices list and zero out the old super
*/
- if (device->writeable) {
+ if (clear_super) {
/* make sure this device isn't detected as part of
* the FS anymore
*/
@@ -1365,8 +1399,6 @@
sync_dirty_buffer(bh);
}
- kfree(device->name);
- kfree(device);
ret = 0;
error_brelse:
@@ -1425,7 +1457,8 @@
mutex_init(&seed_devices->device_list_mutex);
mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
- list_splice_init(&fs_devices->devices, &seed_devices->devices);
+ list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices,
+ synchronize_rcu);
mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
list_splice_init(&fs_devices->alloc_list, &seed_devices->alloc_list);
@@ -1624,7 +1657,7 @@
* half setup
*/
mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
- list_add(&device->dev_list, &root->fs_info->fs_devices->devices);
+ list_add_rcu(&device->dev_list, &root->fs_info->fs_devices->devices);
list_add(&device->dev_alloc_list,
&root->fs_info->fs_devices->alloc_list);
root->fs_info->fs_devices->num_devices++;