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Btrfs: using rcu lock in the reader side of devices list
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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>
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Xiao Guangrong authored and Chris Mason committed May 23, 2011
1 parent 4622470 commit 1f78160
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Showing 4 changed files with 72 additions and 36 deletions.
14 changes: 7 additions & 7 deletions fs/btrfs/disk-io.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1410,8 +1410,8 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
struct btrfs_device *device;
struct backing_dev_info *bdi;

mutex_lock(&info->fs_devices->device_list_mutex);
list_for_each_entry(device, &info->fs_devices->devices, dev_list) {
rcu_read_lock();
list_for_each_entry_rcu(device, &info->fs_devices->devices, dev_list) {
if (!device->bdev)
continue;
bdi = blk_get_backing_dev_info(device->bdev);
Expand All @@ -1420,7 +1420,7 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
break;
}
}
mutex_unlock(&info->fs_devices->device_list_mutex);
rcu_read_unlock();
return ret;
}

Expand Down Expand Up @@ -2332,9 +2332,9 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
sb = &root->fs_info->super_for_commit;
dev_item = &sb->dev_item;

mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
rcu_read_lock();
head = &root->fs_info->fs_devices->devices;
list_for_each_entry(dev, head, dev_list) {
list_for_each_entry_rcu(dev, head, dev_list) {
if (!dev->bdev) {
total_errors++;
continue;
Expand Down Expand Up @@ -2367,7 +2367,7 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
}

total_errors = 0;
list_for_each_entry(dev, head, dev_list) {
list_for_each_entry_rcu(dev, head, dev_list) {
if (!dev->bdev)
continue;
if (!dev->in_fs_metadata || !dev->writeable)
Expand All @@ -2377,7 +2377,7 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
if (ret)
total_errors++;
}
mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
rcu_read_unlock();
if (total_errors > max_errors) {
printk(KERN_ERR "btrfs: %d errors while writing supers\n",
total_errors);
Expand Down
7 changes: 4 additions & 3 deletions fs/btrfs/ioctl.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -281,8 +281,9 @@ static noinline int btrfs_ioctl_fitrim(struct file *file, void __user *arg)
if (!capable(CAP_SYS_ADMIN))
return -EPERM;

mutex_lock(&fs_info->fs_devices->device_list_mutex);
list_for_each_entry(device, &fs_info->fs_devices->devices, dev_list) {
rcu_read_lock();
list_for_each_entry_rcu(device, &fs_info->fs_devices->devices,
dev_list) {
if (!device->bdev)
continue;
q = bdev_get_queue(device->bdev);
Expand All @@ -292,7 +293,7 @@ static noinline int btrfs_ioctl_fitrim(struct file *file, void __user *arg)
minlen);
}
}
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
rcu_read_unlock();
if (!num_devices)
return -EOPNOTSUPP;

Expand Down
85 changes: 59 additions & 26 deletions fs/btrfs/volumes.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -363,7 +363,7 @@ static noinline int device_list_add(const char *path,
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;
Expand Down Expand Up @@ -471,6 +471,29 @@ int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices)
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;
Expand All @@ -480,18 +503,27 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)

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);

Expand Down Expand Up @@ -1204,11 +1236,13 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
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);
Expand Down Expand Up @@ -1294,6 +1328,7 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
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);
Expand All @@ -1304,16 +1339,15 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
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--;

Expand All @@ -1327,36 +1361,36 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
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
*/
Expand All @@ -1365,8 +1399,6 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
sync_dirty_buffer(bh);
}

kfree(device->name);
kfree(device);
ret = 0;

error_brelse:
Expand Down Expand Up @@ -1425,7 +1457,8 @@ static int btrfs_prepare_sprout(struct btrfs_trans_handle *trans,
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);
Expand Down Expand Up @@ -1624,7 +1657,7 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
* 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++;
Expand Down
2 changes: 2 additions & 0 deletions fs/btrfs/volumes.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,8 @@ struct btrfs_device {
u8 uuid[BTRFS_UUID_SIZE];

struct btrfs_work work;
struct rcu_head rcu;
struct work_struct rcu_work;
};

struct btrfs_fs_devices {
Expand Down

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