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Commit 02dbfc99 authored by Omar Sandoval's avatar Omar Sandoval Committed by Chris Mason
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Btrfs: fix ->iterate_shared() by upgrading i_rwsem for delayed nodes 



Commit fe742fd4 ("Revert "btrfs: switch to ->iterate_shared()"")
backed out the conversion to ->iterate_shared() for Btrfs because the
delayed inode handling in btrfs_real_readdir() is racy. However, we can
still do readdir in parallel if there are no delayed nodes.

This is a temporary fix which upgrades the shared inode lock to an
exclusive lock only when we have delayed items until we come up with a
more complete solution. While we're here, rename the
btrfs_{get,put}_delayed_items functions to make it very clear that
they're just for readdir.

Tested with xfstests and by doing a parallel kernel build:

	while make tinyconfig && make -j4 && git clean dqfx; do
		:
	done

along with a bunch of parallel finds in another shell:

	while true; do
		for ((i=0; i<4; i++)); do
			find . >/dev/null &
		done
		wait
	done

Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
parent 33688abb

fs/btrfs/delayed-inode.c

+22 −5
Original line number Diff line number Diff line
@@ -1606,7 +1606,8 @@ int btrfs_inode_delayed_dir_index_count(struct inode *inode) 
	return 0;

}



void btrfs_get_delayed_items(struct inode *inode, struct list_head *ins_list,

bool btrfs_readdir_get_delayed_items(struct inode *inode,

				     struct list_head *ins_list,

				     struct list_head *del_list)

{

	struct btrfs_delayed_node *delayed_node;
@@ -1614,7 +1615,14 @@ void btrfs_get_delayed_items(struct inode *inode, struct list_head *ins_list, 


	delayed_node = btrfs_get_delayed_node(inode);

	if (!delayed_node)

		return;

		return false;



	/*

	 * We can only do one readdir with delayed items at a time because of

	 * item->readdir_list.

	 */

	inode_unlock_shared(inode);

	inode_lock(inode);



	mutex_lock(&delayed_node->mutex);

	item = __btrfs_first_delayed_insertion_item(delayed_node);
@@ -1641,9 +1649,12 @@ void btrfs_get_delayed_items(struct inode *inode, struct list_head *ins_list, 
	 * requeue or dequeue this delayed node.

	 */

	atomic_dec(&delayed_node->refs);



	return true;

}



void btrfs_put_delayed_items(struct list_head *ins_list,

void btrfs_readdir_put_delayed_items(struct inode *inode,

				     struct list_head *ins_list,

				     struct list_head *del_list)

{

	struct btrfs_delayed_item *curr, *next;
@@ -1659,6 +1670,12 @@ void btrfs_put_delayed_items(struct list_head *ins_list, 
		if (atomic_dec_and_test(&curr->refs))

			kfree(curr);

	}



	/*

	 * The VFS is going to do up_read(), so we need to downgrade back to a

	 * read lock.

	 */

	downgrade_write(&inode->i_rwsem);

}



int btrfs_should_delete_dir_index(struct list_head *del_list,

fs/btrfs/delayed-inode.h

+6 −4
Original line number Diff line number Diff line
@@ -137,9 +137,11 @@ void btrfs_kill_all_delayed_nodes(struct btrfs_root *root); 
void btrfs_destroy_delayed_inodes(struct btrfs_root *root);



/* Used for readdir() */

void btrfs_get_delayed_items(struct inode *inode, struct list_head *ins_list,

bool btrfs_readdir_get_delayed_items(struct inode *inode,

				     struct list_head *ins_list,

				     struct list_head *del_list);

void btrfs_put_delayed_items(struct list_head *ins_list,

void btrfs_readdir_put_delayed_items(struct inode *inode,

				     struct list_head *ins_list,

				     struct list_head *del_list);

int btrfs_should_delete_dir_index(struct list_head *del_list,

				  u64 index);

fs/btrfs/inode.c

+6 −4
Original line number Diff line number Diff line
@@ -5757,6 +5757,7 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx) 
	int name_len;

	int is_curr = 0;	/* ctx->pos points to the current index? */

	bool emitted;

	bool put = false;



	/* FIXME, use a real flag for deciding about the key type */

	if (root->fs_info->tree_root == root)
@@ -5774,7 +5775,8 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx) 
	if (key_type == BTRFS_DIR_INDEX_KEY) {

		INIT_LIST_HEAD(&ins_list);

		INIT_LIST_HEAD(&del_list);

		btrfs_get_delayed_items(inode, &ins_list, &del_list);

		put = btrfs_readdir_get_delayed_items(inode, &ins_list,

						      &del_list);

	}



	key.type = key_type;
@@ -5921,8 +5923,8 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx) 
nopos:

	ret = 0;

err:

	if (key_type == BTRFS_DIR_INDEX_KEY)

		btrfs_put_delayed_items(&ins_list, &del_list);

	if (put)

		btrfs_readdir_put_delayed_items(inode, &ins_list, &del_list);

	btrfs_free_path(path);

	return ret;

}
@@ -10534,7 +10536,7 @@ static const struct inode_operations btrfs_dir_ro_inode_operations = { 
static const struct file_operations btrfs_dir_file_operations = {

	.llseek		= generic_file_llseek,

	.read		= generic_read_dir,

	.iterate	= btrfs_real_readdir,

	.iterate_shared	= btrfs_real_readdir,

	.unlocked_ioctl	= btrfs_ioctl,

#ifdef CONFIG_COMPAT

	.compat_ioctl	= btrfs_compat_ioctl,