[PATCH v4 08/15] btrfs: Stop using call_rcu for device freeing

[Nikolay Borisov]

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.

Signed-off-by: Nikolay Borisov <nbori...@suse.com>
---
 fs/btrfs/volumes.c | 20 ++++++++------------
 fs/btrfs/volumes.h |  1 -
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d2d37adbc6fd..90eff8452c31 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1230,14 +1230,6 @@ void btrfs_free_extra_devids(struct btrfs_fs_devices 
*fs_devices, int step)
        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)
@@ -1285,7 +1277,8 @@ 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)
@@ -2242,7 +2235,8 @@ 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) {
@@ -2310,7 +2304,8 @@ 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) {
@@ -2368,7 +2363,8 @@ 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(
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index a0f09aad3770..81784b68ca12 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -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;
-- 
2.17.1