From: Josef Bacik <jbacik@fb.com>
Date: Mon, 24 Jul 2017 15:14:25 -0400
Subject: btrfs: fix readdir deadlock with pagefault
Git-commit: 23b5ec74943f44378b68c0edd8e210a86318ea5e
Patch-mainline: v4.14-rc1
References: bsc#1083000
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.
Thread A
readdir <holding tree lock>
dir_emit
<page fault>
down_read(mmap_sem)
Thread B
mmap write
down_write(mmap_sem)
page_mkwrite
wait_ordered_extents
Process C
finish_ordered_extent
insert_reserved_file_extent
try to lock leaf <hang>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ copy the deadlock scenario to changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
fs/btrfs/ctree.h | 6 +++
fs/btrfs/file.c | 9 ++++
fs/btrfs/inode.c | 106 ++++++++++++++++++++++++++++++++++++++++++++-----------
fs/btrfs/ioctl.c | 22 +++++++----
4 files changed, 114 insertions(+), 29 deletions(-)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1277,6 +1277,12 @@ struct btrfs_root {
/* For qgroup metadata space reserve */
atomic64_t qgroup_meta_rsv;
};
+
+struct btrfs_file_private {
+ struct btrfs_trans_handle *trans;
+ void *filldir_buf;
+};
+
static inline u32 btrfs_inode_sectorsize(const struct inode *inode)
{
return btrfs_sb(inode->i_sb)->sectorsize;
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1984,8 +1984,15 @@ out:
int btrfs_release_file(struct inode *inode, struct file *filp)
{
- if (filp->private_data)
+ struct btrfs_file_private *private = filp->private_data;
+
+ if (private && private->trans)
btrfs_ioctl_trans_end(filp);
+ if (private && private->filldir_buf)
+ kfree(private->filldir_buf);
+ kfree(private);
+ filp->private_data = NULL;
+
/*
* ordered_data_close is set by settattr when we are about to truncate
* a file from a non-zero size to a zero size. This tries to
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5862,26 +5862,78 @@ 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 mess 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 btrfs_file_private *private;
+
+ private = kzalloc(sizeof(struct btrfs_file_private), GFP_KERNEL);
+ if (!private)
+ return -ENOMEM;
+ private->filldir_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!private->filldir_buf) {
+ kfree(private);
+ return -ENOMEM;
+ }
+ file->private_data = private;
+ 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;
+ addr += sizeof(struct dir_entry) + entry->name_len;
+ ctx->pos++;
+ }
+ return 0;
+}
+
+
+
static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
{
struct inode *inode = file_inode(file);
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
struct btrfs_root *root = BTRFS_I(inode)->root;
+ struct btrfs_file_private *private = file->private_data;
struct btrfs_item *item;
struct btrfs_dir_item *di;
struct btrfs_key key;
struct btrfs_key found_key;
struct btrfs_path *path;
+ void *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;
@@ -5892,12 +5944,14 @@ static int btrfs_real_readdir(struct fil
if (!path)
return -ENOMEM;
+ addr = private->filldir_buf;
path->reada = READA_FORWARD;
INIT_LIST_HEAD(&ins_list);
INIT_LIST_HEAD(&del_list);
put = btrfs_readdir_get_delayed_items(inode, &ins_list, &del_list);
+again:
key.type = BTRFS_DIR_INDEX_KEY;
key.offset = ctx->pos;
key.objectid = btrfs_ino(BTRFS_I(inode));
@@ -5907,6 +5961,8 @@ static int btrfs_real_readdir(struct fil
goto err;
while (1) {
+ struct dir_entry *entry;
+
leaf = path->nodes[0];
slot = path->slots[0];
if (slot >= btrfs_header_nritems(leaf)) {
@@ -5937,34 +5993,41 @@ static int btrfs_real_readdir(struct fil
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(private->filldir_buf, entries, ctx);
+ if (ret)
+ goto nopos;
+ addr = private->filldir_buf;
+ entries = 0;
+ total_len = 0;
+ goto again;
}
+ 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);
+ 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;
- 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++;
next:
path->slots[0]++;
}
+ btrfs_release_path(path);
+
+ ret = btrfs_filldir(private->filldir_buf, entries, ctx);
+ if (ret)
+ goto nopos;
+
ret = btrfs_readdir_delayed_dir_index(ctx, &ins_list);
if (ret)
goto nopos;
@@ -10664,6 +10727,7 @@ static const struct file_operations btrf
.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,
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3995,6 +3995,7 @@ static long btrfs_ioctl_trans_start(stru
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
struct btrfs_root *root = BTRFS_I(inode)->root;
struct btrfs_trans_handle *trans;
+ struct btrfs_file_private *private;
int ret;
ret = -EPERM;
@@ -4002,8 +4003,16 @@ static long btrfs_ioctl_trans_start(stru
goto out;
ret = -EINPROGRESS;
- if (file->private_data)
+ private = file->private_data;
+ if (private && private->trans)
goto out;
+ if (!private) {
+ private = kzalloc(sizeof(struct btrfs_file_private),
+ GFP_KERNEL);
+ if (!private)
+ return -ENOMEM;
+ file->private_data = private;
+ }
ret = -EROFS;
if (btrfs_root_readonly(root))
@@ -4020,7 +4029,7 @@ static long btrfs_ioctl_trans_start(stru
if (IS_ERR(trans))
goto out_drop;
- file->private_data = trans;
+ private->trans = trans;
return 0;
out_drop:
@@ -4275,14 +4284,13 @@ long btrfs_ioctl_trans_end(struct file *
{
struct inode *inode = file_inode(file);
struct btrfs_root *root = BTRFS_I(inode)->root;
- struct btrfs_trans_handle *trans;
+ struct btrfs_file_private *private = file->private_data;
- trans = file->private_data;
- if (!trans)
+ if (!private || !private->trans)
return -EINVAL;
- file->private_data = NULL;
- btrfs_end_transaction(trans);
+ btrfs_end_transaction(private->trans);
+ private->trans = NULL;
atomic_dec(&root->fs_info->open_ioctl_trans);