From: Josef Bacik <jba...@fb.com>
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 <jba...@fb.com>
---
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) {
+ 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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