[PATCH 3.16 044/245] btrfs: tree-checker: Fix false panic for sanity test

Ben Hutchings
2020-04-23T23:22:09Z

From: Qu Wenruo <wqu@suse.com>

commit 69fc6cbbac542c349b3d350d10f6e394c253c81d upstream.

[BUG]
If we run btrfs with CONFIG_BTRFS_FS_RUN_SANITY_TESTS=y, it will
instantly cause kernel panic like:

------
...
assertion failed: 0, file: fs/btrfs/disk-io.c, line: 3853
...
Call Trace:
btrfs_mark_buffer_dirty+0x187/0x1f0 [btrfs]
setup_items_for_insert+0x385/0x650 [btrfs]
__btrfs_drop_extents+0x129a/0x1870 [btrfs]
...
-----

[Cause]
Btrfs will call btrfs_check_leaf() in btrfs_mark_buffer_dirty() to check
if the leaf is valid with CONFIG_BTRFS_FS_RUN_SANITY_TESTS=y.

However quite some btrfs_mark_buffer_dirty() callers(*) don't really
initialize its item data but only initialize its item pointers, leaving
item data uninitialized.

This makes tree-checker catch uninitialized data as error, causing
such panic.

*: These callers include but not limited to
setup_items_for_insert()
btrfs_split_item()
btrfs_expand_item()

[Fix]
Add a new parameter @check_item_data to btrfs_check_leaf().
With @check_item_data set to false, item data check will be skipped and
fallback to old btrfs_check_leaf() behavior.

So we can still get early warning if we screw up item pointers, and
avoid false panic.

Cc: Filipe Manana <fdmanana@gmail.com>
Reported-by: Lakshmipathi.G <lakshmipathi.g@gmail.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[bwh: Backported to 4.4: adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/btrfs/disk-io.c | 10 ++++++++--
fs/btrfs/tree-checker.c | 27 ++++++++++++++++++++++-----
fs/btrfs/tree-checker.h | 14 +++++++++++++-
3 files changed, 43 insertions(+), 8 deletions(-)

--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -575,7 +575,7 @@ static int btree_readpage_end_io_hook(st
* that we don't try and read the other copies of this block, just
* return -EIO.
*/
- if (found_level == 0 && btrfs_check_leaf(root, eb)) {
+ if (found_level == 0 && btrfs_check_leaf_full(root, eb)) {
set_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags);
ret = -EIO;
}
@@ -3702,7 +3702,13 @@ void btrfs_mark_buffer_dirty(struct exte
buf->len,
root->fs_info->dirty_metadata_batch);
#ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
- if (btrfs_header_level(buf) == 0 && btrfs_check_leaf(root, buf)) {
+ /*
+ * Since btrfs_mark_buffer_dirty() can be called with item pointer set
+ * but item data not updated.
+ * So here we should only check item pointers, not item data.
+ */
+ if (btrfs_header_level(buf) == 0 &&
+ btrfs_check_leaf_relaxed(root, buf)) {
btrfs_print_leaf(root, buf);
ASSERT(0);
}
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -195,7 +195,8 @@ static int check_leaf_item(struct btrfs_
return ret;
}

-int btrfs_check_leaf(struct btrfs_root *root, struct extent_buffer *leaf)
+static int check_leaf(struct btrfs_root *root, struct extent_buffer *leaf,
+ bool check_item_data)
{
struct btrfs_fs_info *fs_info = root->fs_info;
/* No valid key type is 0, so all key should be larger than this key */
@@ -299,10 +300,15 @@ int btrfs_check_leaf(struct btrfs_root *
return -EUCLEAN;
}

- /* Check if the item size and content meet other criteria */
- ret = check_leaf_item(root, leaf, &key, slot);
- if (ret < 0)
- return ret;
+ if (check_item_data) {
+ /*
+ * Check if the item size and content meet other
+ * criteria
+ */
+ ret = check_leaf_item(root, leaf, &key, slot);
+ if (ret < 0)
+ return ret;
+ }

prev_key.objectid = key.objectid;
prev_key.type = key.type;
@@ -312,6 +318,17 @@ int btrfs_check_leaf(struct btrfs_root *
return 0;
}

+int btrfs_check_leaf_full(struct btrfs_root *root, struct extent_buffer *leaf)
+{
+ return check_leaf(root, leaf, true);
+}
+
+int btrfs_check_leaf_relaxed(struct btrfs_root *root,
+ struct extent_buffer *leaf)
+{
+ return check_leaf(root, leaf, false);
+}
+
int btrfs_check_node(struct btrfs_root *root, struct extent_buffer *node)
{
unsigned long nr = btrfs_header_nritems(node);
--- a/fs/btrfs/tree-checker.h
+++ b/fs/btrfs/tree-checker.h
@@ -20,7 +20,19 @@
#include "ctree.h"
#include "extent_io.h"

-int btrfs_check_leaf(struct btrfs_root *root, struct extent_buffer *leaf);
+/*
+ * Comprehensive leaf checker.
+ * Will check not only the item pointers, but also every possible member
+ * in item data.
+ */
+int btrfs_check_leaf_full(struct btrfs_root *root, struct extent_buffer *leaf);
+
+/*
+ * Less strict leaf checker.
+ * Will only check item pointers, not reading item data.
+ */
+int btrfs_check_leaf_relaxed(struct btrfs_root *root,
+ struct extent_buffer *leaf);
int btrfs_check_node(struct btrfs_root *root, struct extent_buffer *node);

#endif