Commit fede766f authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: avoid deadlocks from GFP_KERNEL allocations during btrfs_real_readdir 



Btrfs has an optimization where it will preallocate dentries during
readdir to fill in enough information to open the inode without an extra
lookup.

But, we're calling d_alloc, which is doing GFP_KERNEL allocations, and
that leads to deadlocks because our readdir code has tree locks held.

For now, disable this optimization.  We'll fix the gfp mask in the next
merge window.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 7654b724

fs/btrfs/inode.c

+1 −29
Original line number Diff line number Diff line
@@ -4192,7 +4192,6 @@ static int btrfs_real_readdir(struct file *filp, void *dirent, 
	struct btrfs_path *path;

	struct list_head ins_list;

	struct list_head del_list;

	struct qstr q;

	int ret;

	struct extent_buffer *leaf;

	int slot;
@@ -4283,7 +4282,6 @@ static int btrfs_real_readdir(struct file *filp, void *dirent, 


		while (di_cur < di_total) {

			struct btrfs_key location;

			struct dentry *tmp;



			if (verify_dir_item(root, leaf, di))

				break;
@@ -4304,33 +4302,7 @@ static int btrfs_real_readdir(struct file *filp, void *dirent, 
			d_type = btrfs_filetype_table[btrfs_dir_type(leaf, di)];

			btrfs_dir_item_key_to_cpu(leaf, di, &location);



			q.name = name_ptr;

			q.len = name_len;

			q.hash = full_name_hash(q.name, q.len);

			tmp = d_lookup(filp->f_dentry, &q);

			if (!tmp) {

				struct btrfs_key *newkey;



				newkey = kzalloc(sizeof(struct btrfs_key),

						 GFP_NOFS);

				if (!newkey)

					goto no_dentry;

				tmp = d_alloc(filp->f_dentry, &q);

				if (!tmp) {

					kfree(newkey);

					dput(tmp);

					goto no_dentry;

				}

				memcpy(newkey, &location,

				       sizeof(struct btrfs_key));

				tmp->d_fsdata = newkey;

				tmp->d_flags |= DCACHE_NEED_LOOKUP;

				d_rehash(tmp);

				dput(tmp);

			} else {

				dput(tmp);

			}

no_dentry:

			/* is this a reference to our own snapshot? If so

			 * skip it.

			 *

CRA Git | Maintained and supported by SUSTech CRA and CCSE