On Fri, Jul 21, 2017 at 01:29:08PM -0400, josef@xxxxxxxxxxxxxx wrote:
> From: Josef Bacik <jbacik@xxxxxx>
>
> Readdir does dir_emit while under the btree lock. dir_emit can trigger
> the page fault which means we can deadlock. Fix this by allocating a
> buffer on opening a directory and copying the readdir into this buffer
> and doing dir_emit from outside of the tree lock.
>
> Signed-off-by: Josef Bacik <jbacik@xxxxxx>
> ---
> fs/btrfs/inode.c | 110 +++++++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 83 insertions(+), 27 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 9a4413a..61396e3 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -5877,6 +5877,56 @@ unsigned char btrfs_filetype_table[] = {
> DT_UNKNOWN, DT_REG, DT_DIR, DT_CHR, DT_BLK, DT_FIFO, DT_SOCK, DT_LNK
> };
>
> +/*
> + * All this infrastructure exists because dir_emit can fault, and we are holding
> + * the tree lock when doing readdir. For now just allocate a buffer and copy
> + * our information into that, and then dir_emit from the buffer. This is
> + * similar to what NFS does, only we don't keep the buffer around in pagecache
> + * because I'm afraid I'll fuck that up. Long term we need to make filldir do
> + * copy_to_user_inatomic so we don't have to worry about page faulting under the
> + * tree lock.
> + */
> +static int btrfs_opendir(struct inode *inode, struct file *file)
> +{
> + struct page *page;
> +
> + page = alloc_page(GFP_KERNEL);
> + if (!page)
> + return -ENOMEM;
> + file->private_data = page;
> + return 0;
> +}
> +
> +static int btrfs_closedir(struct inode *inode, struct file *file)
> +{
> + if (file->private_data) {
> + __free_page((struct page *)file->private_data);
> + file->private_data = NULL;
> + }
> + return 0;
> +}
> +
> +struct dir_entry {
> + u64 ino;
> + u64 offset;
> + unsigned type;
> + int name_len;
> +};
> +
> +static int btrfs_filldir(void *addr, int entries, struct dir_context *ctx)
> +{
> + while (entries--) {
> + struct dir_entry *entry = addr;
> + char *name = (char *)(entry + 1);
> + ctx->pos = entry->offset;
> + if (!dir_emit(ctx, name, entry->name_len, entry->ino,
> + entry->type))
> + return 1;
> + ctx->pos++;
> + }
> + return 0;
> +}
> +
> static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
> {
> struct inode *inode = file_inode(file);
> @@ -5886,16 +5936,17 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
> struct btrfs_key key;
> struct btrfs_key found_key;
> struct btrfs_path *path;
> + struct page *page = file->private_data;
> + void *addr, *start_addr;
> struct list_head ins_list;
> struct list_head del_list;
> int ret;
> struct extent_buffer *leaf;
> int slot;
> - unsigned char d_type;
> - int over = 0;
> - char tmp_name[32];
> char *name_ptr;
> int name_len;
> + int entries = 0;
> + int total_len = 0;
> bool put = false;
> struct btrfs_key location;
>
> @@ -5906,6 +5957,7 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
> if (!path)
> return -ENOMEM;
>
> + start_addr = addr = kmap(page);
> path->reada = READA_FORWARD;
>
> INIT_LIST_HEAD(&ins_list);
> @@ -5921,6 +5973,7 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
> goto err;
>
> while (1) {
> + struct dir_entry *entry;
> leaf = path->nodes[0];
> slot = path->slots[0];
> if (slot >= btrfs_header_nritems(leaf)) {
> @@ -5942,41 +5995,42 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
> goto next;
> if (btrfs_should_delete_dir_index(&del_list, found_key.offset))
> goto next;
> -
> - ctx->pos = found_key.offset;
> -
> di = btrfs_item_ptr(leaf, slot, struct btrfs_dir_item);
> if (verify_dir_item(fs_info, leaf, slot, di))
> goto next;
>
> name_len = btrfs_dir_name_len(leaf, di);
> - if (name_len <= sizeof(tmp_name)) {
> - name_ptr = tmp_name;
> - } else {
> - name_ptr = kmalloc(name_len, GFP_KERNEL);
> - if (!name_ptr) {
> - ret = -ENOMEM;
> - goto err;
> - }
> + if ((total_len + sizeof(struct dir_entry) + name_len) >=
> + PAGE_SIZE) {
How does this work for filenames that of PATH_MAX length? Regardless of
total_len size, the rest will always overflow PAGE_SIZE if it's 4k.
> + btrfs_release_path(path);
> + ret = btrfs_filldir(start_addr, entries, ctx);
> + if (ret)
> + goto nopos;
> + addr = start_addr;
> + entries = 0;
> + total_len = 0;
> }
> +
> + entry = addr;
> + entry->name_len = name_len;
> + name_ptr = (char *)(entry + 1);
> read_extent_buffer(leaf, name_ptr, (unsigned long)(di + 1),
> name_len);
> -
> - d_type = btrfs_filetype_table[btrfs_dir_type(leaf, di)];
> + entry->type = btrfs_filetype_table[btrfs_dir_type(leaf, di)];
> btrfs_dir_item_key_to_cpu(leaf, di, &location);
> -
> - over = !dir_emit(ctx, name_ptr, name_len, location.objectid,
> - d_type);
> -
> - if (name_ptr != tmp_name)
> - kfree(name_ptr);
> -
> - if (over)
> - goto nopos;
> - ctx->pos++;
> + entry->ino = location.objectid;
> + entry->offset = found_key.offset;
> + entries++;
> + addr += sizeof(struct dir_entry) + name_len;
> + total_len += sizeof(struct dir_entry) + name_len;
> next:
> path->slots[0]++;
> }
> + btrfs_release_path(path);
> +
> + ret = btrfs_filldir(start_addr, entries, ctx);
> + if (ret)
> + goto nopos;
>
> ret = btrfs_readdir_delayed_dir_index(ctx, &ins_list);
> if (ret)
> @@ -6006,6 +6060,7 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
> nopos:
> ret = 0;
> err:
> + kunmap(page);
> if (put)
> btrfs_readdir_put_delayed_items(inode, &ins_list, &del_list);
> btrfs_free_path(path);
> @@ -10777,11 +10832,12 @@ static const struct file_operations btrfs_dir_file_operations = {
> .llseek = generic_file_llseek,
> .read = generic_read_dir,
> .iterate_shared = btrfs_real_readdir,
> + .open = btrfs_opendir,
> .unlocked_ioctl = btrfs_ioctl,
> #ifdef CONFIG_COMPAT
> .compat_ioctl = btrfs_compat_ioctl,
> #endif
> - .release = btrfs_release_file,
> + .release = btrfs_closedir,
> .fsync = btrfs_sync_file,
> };
>
> --
> 2.7.4
>
> --
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