mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-09-22 22:11:38 +08:00
6f932d4ef0
A call to btrfs_prev_leaf() may end up returning a path that points to the
same item (key) again. This happens if while btrfs_prev_leaf(), after we
release the path, a concurrent insertion happens, which moves items off
from a sibling into the front of the previous leaf, and an item with the
computed previous key does not exists.
For example, suppose we have the two following leaves:
Leaf A
-------------------------------------------------------------
| ... key (300 96 10) key (300 96 15) key (300 96 16) |
-------------------------------------------------------------
slot 20 slot 21 slot 22
Leaf B
-------------------------------------------------------------
| key (300 96 20) key (300 96 21) key (300 96 22) ... |
-------------------------------------------------------------
slot 0 slot 1 slot 2
If we call btrfs_prev_leaf(), from btrfs_previous_item() for example, with
a path pointing to leaf B and slot 0 and the following happens:
1) At btrfs_prev_leaf() we compute the previous key to search as:
(300 96 19), which is a key that does not exists in the tree;
2) Then we call btrfs_release_path() at btrfs_prev_leaf();
3) Some other task inserts a key at leaf A, that sorts before the key at
slot 20, for example it has an objectid of 299. In order to make room
for the new key, the key at slot 22 is moved to the front of leaf B.
This happens at push_leaf_right(), called from split_leaf().
After this leaf B now looks like:
--------------------------------------------------------------------------------
| key (300 96 16) key (300 96 20) key (300 96 21) key (300 96 22) ... |
--------------------------------------------------------------------------------
slot 0 slot 1 slot 2 slot 3
4) At btrfs_prev_leaf() we call btrfs_search_slot() for the computed
previous key: (300 96 19). Since the key does not exists,
btrfs_search_slot() returns 1 and with a path pointing to leaf B
and slot 1, the item with key (300 96 20);
5) This makes btrfs_prev_leaf() return a path that points to slot 1 of
leaf B, the same key as before it was called, since the key at slot 0
of leaf B (300 96 16) is less than the computed previous key, which is
(300 96 19);
6) As a consequence btrfs_previous_item() returns a path that points again
to the item with key (300 96 20).
For some users of btrfs_prev_leaf() or btrfs_previous_item() this may not
be functional a problem, despite not making sense to return a new path
pointing again to the same item/key. However for a caller such as
tree-log.c:log_dir_items(), this has a bad consequence, as it can result
in not logging some dir index deletions in case the directory is being
logged without holding the inode's VFS lock (logging triggered while
logging a child inode for example) - for the example scenario above, in
case the dir index keys 17, 18 and 19 were deleted in the current
transaction.
CC: stable@vger.kernel.org # 4.14+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.