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btrfs: Stop using call_rcu for device freeing 

btrfs_device structs are freed from RCU context since device iteration
is protected by RCU. Currently this is achieved by using call_rcu since
no blocking functions are called within btrfs_free_device. Future
refactoring of pending/pinned chunks will require calling sleeping
functions.

This patch is in preparation for these changes by simply switching from
RCU callbacks to explicit calls of synchronize_rcu and calling
btrfs_free_device directly. This is functionally equivalent, making sure
that there are no readers at that time.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Nikolay Borisov 2019-03-27 14:24:11 +02:00 committed by David Sterba
parent 4ca7365606
commit 8e75fd893b
2 changed files with 8 additions and 13 deletions
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20
fs/btrfs/volumes.c
View File

@ -1231,14 +1231,6 @@ again:
mutex_unlock(&uuid_mutex);
}
static void free_device_rcu(struct rcu_head *head)
{
struct btrfs_device *device;
device = container_of(head, struct btrfs_device, rcu);
btrfs_free_device(device);
}
static void btrfs_close_bdev(struct btrfs_device *device)
{
if (!device->bdev)
@ -1286,7 +1278,8 @@ static void btrfs_close_one_device(struct btrfs_device *device)
list_replace_rcu(&device->dev_list, &new_device->dev_list);
new_device->fs_devices = device->fs_devices;
call_rcu(&device->rcu, free_device_rcu);
synchronize_rcu();
btrfs_free_device(device);
}
static int close_fs_devices(struct btrfs_fs_devices *fs_devices)
@ -2243,7 +2236,8 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
btrfs_scratch_superblocks(device->bdev, device->name->str);
btrfs_close_bdev(device);
call_rcu(&device->rcu, free_device_rcu);
synchronize_rcu();
btrfs_free_device(device);
if (cur_devices->open_devices == 0) {
while (fs_devices) {
@ -2311,7 +2305,8 @@ void btrfs_rm_dev_replace_free_srcdev(struct btrfs_fs_info *fs_info,
}
btrfs_close_bdev(srcdev);
call_rcu(&srcdev->rcu, free_device_rcu);
synchronize_rcu();
btrfs_free_device(srcdev);
/* if this is no devs we rather delete the fs_devices */
if (!fs_devices->num_devices) {
@ -2369,7 +2364,8 @@ void btrfs_destroy_dev_replace_tgtdev(struct btrfs_device *tgtdev)
btrfs_scratch_superblocks(tgtdev->bdev, tgtdev->name->str);
btrfs_close_bdev(tgtdev);
call_rcu(&tgtdev->rcu, free_device_rcu);
synchronize_rcu();
btrfs_free_device(tgtdev);
}
static struct btrfs_device *btrfs_find_device_by_path(

1
fs/btrfs/volumes.h
View File

@ -118,7 +118,6 @@ struct btrfs_device {
struct scrub_ctx *scrub_ctx;
struct btrfs_work work;
struct rcu_head rcu;
/* readahead state */
atomic_t reada_in_flight;