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btrfs: use async_chunk::async_cow to replace the confusing pending pointer

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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.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2021-09-27 15:21:45 +08:00 committed by David Sterba
parent cf3075fb36
commit 9e895a8f7e
1 changed files with 7 additions and 9 deletions
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16
fs/btrfs/inode.c
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@ -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[];
};
@ -1324,18 +1323,17 @@ 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,
@ -1396,7 +1394,7 @@ 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;