diff mbox series

[3/4] btrfs: kill the rcu protection for fs_info->space_info

Message ID a88fca8411a0b1f5bc25926a4489b07af0f65ffa.1598996236.git.josef@toxicpanda.com (mailing list archive)
State New, archived
Headers show
Series Lockdep fixes | expand

Commit Message

Josef Bacik Sept. 1, 2020, 9:40 p.m. UTC 
We have this thing wrapped in an rcu lock, but it's really not needed.
We create all the space_info's on mount, and we destroy them on unmount.
The list never changes and we're protected from messing with it by the
normal mount/umount path, so kill the RCU stuff around it.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/block-group.c | 16 ++--------------
 fs/btrfs/ioctl.c       | 10 ++--------
 fs/btrfs/space-info.c  | 14 ++++----------
 fs/btrfs/super.c       |  5 +----
 4 files changed, 9 insertions(+), 36 deletions(-)

Comments

Nikolay Borisov Sept. 2, 2020, 8:04 a.m. UTC | #1 
On 2.09.20 г. 0:40 ч., Josef Bacik wrote:
> We have this thing wrapped in an rcu lock, but it's really not needed.
> We create all the space_info's on mount, and we destroy them on unmount.
> The list never changes and we're protected from messing with it by the
> normal mount/umount path, so kill the RCU stuff around it.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
David Sterba Sept. 2, 2020, 10:32 a.m. UTC | #2 
On Tue, Sep 01, 2020 at 05:40:37PM -0400, Josef Bacik wrote:
> We have this thing wrapped in an rcu lock, but it's really not needed.
> We create all the space_info's on mount, and we destroy them on unmount.
> The list never changes and we're protected from messing with it by the
> normal mount/umount path, so kill the RCU stuff around it.

What happens when balance filter converts one profile to a new one?
That's neither mount nor umount and it modifies the space infos, so
the RCU is there to keep the consistent view in case statfs/ioctl
happens, no?
diff mbox series

Patch

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 01e8ba1da1d3..a3b27204371c 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2031,8 +2031,7 @@  int btrfs_read_block_groups(struct btrfs_fs_info *info)
 		btrfs_release_path(path);
 	}
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(space_info, &info->space_info, list) {
+	list_for_each_entry(space_info, &info->space_info, list) {
 		if (!(btrfs_get_alloc_profile(info, space_info->flags) &
 		      (BTRFS_BLOCK_GROUP_RAID10 |
 		       BTRFS_BLOCK_GROUP_RAID1_MASK |
@@ -2052,7 +2051,6 @@  int btrfs_read_block_groups(struct btrfs_fs_info *info)
 				list)
 			inc_block_group_ro(cache, 1);
 	}
-	rcu_read_unlock();
 
 	btrfs_init_global_block_rsv(info);
 	ret = check_chunk_block_group_mappings(info);
@@ -3007,12 +3005,10 @@  static void force_metadata_allocation(struct btrfs_fs_info *info)
 	struct list_head *head = &info->space_info;
 	struct btrfs_space_info *found;
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(found, head, list) {
+	list_for_each_entry(found, head, list) {
 		if (found->flags & BTRFS_BLOCK_GROUP_METADATA)
 			found->force_alloc = CHUNK_ALLOC_FORCE;
 	}
-	rcu_read_unlock();
 }
 
 static int should_alloc_chunk(struct btrfs_fs_info *fs_info,
@@ -3343,14 +3339,6 @@  int btrfs_free_block_groups(struct btrfs_fs_info *info)
 	}
 	spin_unlock(&info->block_group_cache_lock);
 
-	/*
-	 * Now that all the block groups are freed, go through and free all the
-	 * space_info structs.  This is only called during the final stages of
-	 * unmount, and so we know nobody is using them.  We call
-	 * synchronize_rcu() once before we start, just to be on the safe side.
-	 */
-	synchronize_rcu();
-
 	btrfs_release_global_block_rsv(info);
 
 	while (!list_empty(&info->space_info)) {
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index a5f466d23139..3a7a34cf6c22 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3461,15 +3461,12 @@  static long btrfs_ioctl_space_info(struct btrfs_fs_info *fs_info,
 		struct btrfs_space_info *tmp;
 
 		info = NULL;
-		rcu_read_lock();
-		list_for_each_entry_rcu(tmp, &fs_info->space_info,
-					list) {
+		list_for_each_entry(tmp, &fs_info->space_info, list) {
 			if (tmp->flags == types[i]) {
 				info = tmp;
 				break;
 			}
 		}
-		rcu_read_unlock();
 
 		if (!info)
 			continue;
@@ -3517,15 +3514,12 @@  static long btrfs_ioctl_space_info(struct btrfs_fs_info *fs_info,
 			break;
 
 		info = NULL;
-		rcu_read_lock();
-		list_for_each_entry_rcu(tmp, &fs_info->space_info,
-					list) {
+		list_for_each_entry(tmp, &fs_info->space_info, list) {
 			if (tmp->flags == types[i]) {
 				info = tmp;
 				break;
 			}
 		}
-		rcu_read_unlock();
 
 		if (!info)
 			continue;
diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index b733718f45d3..837615702c94 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -175,10 +175,8 @@  void btrfs_clear_space_info_full(struct btrfs_fs_info *info)
 	struct list_head *head = &info->space_info;
 	struct btrfs_space_info *found;
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(found, head, list)
+	list_for_each_entry(found, head, list)
 		found->full = 0;
-	rcu_read_unlock();
 }
 
 static int create_space_info(struct btrfs_fs_info *info, u64 flags)
@@ -213,7 +211,7 @@  static int create_space_info(struct btrfs_fs_info *info, u64 flags)
 	if (ret)
 		return ret;
 
-	list_add_rcu(&space_info->list, &info->space_info);
+	list_add(&space_info->list, &info->space_info);
 	if (flags & BTRFS_BLOCK_GROUP_DATA)
 		info->data_sinfo = space_info;
 
@@ -290,14 +288,10 @@  struct btrfs_space_info *btrfs_find_space_info(struct btrfs_fs_info *info,
 
 	flags &= BTRFS_BLOCK_GROUP_TYPE_MASK;
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(found, head, list) {
-		if (found->flags & flags) {
-			rcu_read_unlock();
+	list_for_each_entry(found, head, list) {
+		if (found->flags & flags)
 			return found;
-		}
 	}
-	rcu_read_unlock();
 	return NULL;
 }
 
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 3ebe7240c63d..8840a4fa81eb 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2164,8 +2164,7 @@  static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	u64 thresh = 0;
 	int mixed = 0;
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(found, &fs_info->space_info, list) {
+	list_for_each_entry(found, &fs_info->space_info, list) {
 		if (found->flags & BTRFS_BLOCK_GROUP_DATA) {
 			int i;
 
@@ -2194,8 +2193,6 @@  static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 		total_used += found->disk_used;
 	}
 
-	rcu_read_unlock();
-
 	buf->f_blocks = div_u64(btrfs_super_total_bytes(disk_super), factor);
 	buf->f_blocks >>= bits;
 	buf->f_bfree = buf->f_blocks - (div_u64(total_used, factor) >> bits);