[PATCH v2 03/26] btrfs: use async_chunk::async_cow to replace the confusing pending pointer
From: Qu Wenruo <hidden>
Date: 2021-08-29 05:25:09
Subsystem:
btrfs file system, filesystems (vfs and infrastructure), the rest · Maintainers:
Chris Mason, David Sterba, Alexander Viro, Christian Brauner, Linus Torvalds
For structure async_chunk, we use a very strange member layout to grab structure async_cow who owns this async_chunk. At initialization, it goes like this: async_chunk[i].pending = &ctx->num_chunks; Then at async_cow_free() we do a super weird freeing: /* * Since the pointer to 'pending' is at the beginning of the array of * async_chunk's, freeing it ensures the whole array has been freed. */ if (atomic_dec_and_test(async_chunk->pending)) kvfree(async_chunk->pending); This is absolutely an abuse of kvfree(). Replace async_chunk::pending with async_chunk::async_cow, so that we can grab the async_cow structure directly, without this strange dancing. And with this change, there is no requirement for any specific member location. Signed-off-by: Qu Wenruo <redacted> --- fs/btrfs/inode.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 0517f31a3bed..02448857b72f 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c@@ -455,11 +455,10 @@ struct async_chunk { struct list_head extents; struct cgroup_subsys_state *blkcg_css; struct btrfs_work work; - atomic_t *pending; + struct async_cow *async_cow; }; struct async_cow { - /* Number of chunks in flight; must be first in the structure */ atomic_t num_chunks; struct async_chunk chunks[]; };
@@ -1325,18 +1324,17 @@ static noinline void async_cow_submit(struct btrfs_work *work) static noinline void async_cow_free(struct btrfs_work *work) { struct async_chunk *async_chunk; + struct async_cow *async_cow; async_chunk = container_of(work, struct async_chunk, work); if (async_chunk->inode) btrfs_add_delayed_iput(async_chunk->inode); if (async_chunk->blkcg_css) css_put(async_chunk->blkcg_css); - /* - * Since the pointer to 'pending' is at the beginning of the array of - * async_chunk's, freeing it ensures the whole array has been freed. - */ - if (atomic_dec_and_test(async_chunk->pending)) - kvfree(async_chunk->pending); + + async_cow = async_chunk->async_cow; + if (atomic_dec_and_test(&async_cow->num_chunks)) + kvfree(async_cow); } static int cow_file_range_async(struct btrfs_inode *inode,
@@ -1397,7 +1395,7 @@ static int cow_file_range_async(struct btrfs_inode *inode, * lightweight reference for the callback lifetime */ ihold(&inode->vfs_inode); - async_chunk[i].pending = &ctx->num_chunks; + async_chunk[i].async_cow = ctx; async_chunk[i].inode = &inode->vfs_inode; async_chunk[i].start = start; async_chunk[i].end = cur_end;
--
2.32.0