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When checking if we need to log the new name of a renamed inode, we are checking if the inode and its parent inode have been logged before, and if not we don't log the new name. The check however is buggy, as it directly compares the logged_trans field of the inodes versus the ID of the current transaction. The problem is that logged_trans is a transient field, only stored in memory and never persisted in the inode item, so if an inode was logged before, evicted and reloaded, its logged_trans field is set to a value of 0, meaning the check will return false and the new name of the renamed inode is not logged. If the old parent directory was previously fsynced and we deleted the logged directory entries corresponding to the old name, we end up with a log that when replayed will delete the renamed inode. The following example triggers the problem: $ mkfs.btrfs -f /dev/sdc $ mount /dev/sdc /mnt $ mkdir /mnt/A $ mkdir /mnt/B $ echo -n "hello world" > /mnt/A/foo $ sync # Add some new file to A and fsync directory A. $ touch /mnt/A/bar $ xfs_io -c "fsync" /mnt/A # Now trigger inode eviction. We are only interested in triggering # eviction for the inode of directory A. $ echo 2 > /proc/sys/vm/drop_caches # Move foo from directory A to directory B. # This deletes the directory entries for foo in A from the log, and # does not add the new name for foo in directory B to the log, because # logged_trans of A is 0, which is less than the current transaction ID. $ mv /mnt/A/foo /mnt/B/foo # Now make an fsync to anything except A, B or any file inside them, # like for example create a file at the root directory and fsync this # new file. This syncs the log that contains all the changes done by # previous rename operation. $ touch /mnt/baz $ xfs_io -c "fsync" /mnt/baz <power fail> # Mount the filesystem and replay the log. $ mount /dev/sdc /mnt # Check the filesystem content. $ ls -1R /mnt /mnt/: A B baz /mnt/A: bar /mnt/B: $ # File foo is gone, it's neither in A/ nor in B/. Fix this by using the inode_logged() helper at btrfs_log_new_name(), which safely checks if an inode was logged before in the current transaction. A test case for fstests will follow soon. CC: stable@vger.kernel.org # 4.14+ Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
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| .gitignore | ||
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| COPYING | ||
| CREDITS | ||
| Kbuild | ||
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| 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.