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6d3d970b27
When logging a directory, at log_dir_items(), if we get an error when
attempting to search the subvolume tree for a dir index item, we end up
returning 0 (success) from log_dir_items() because 'err' is left with a
value of 0.
This can lead to a few problems, specially in the case the variable
'last_offset' has a value of (u64)-1 (and it's initialized to that when
it was declared):
1) By returning from log_dir_items() with success (0) and a value of
(u64)-1 for '*last_offset_ret', we end up not logging any other dir
index keys that follow the missing, just deleted, index key. The
(u64)-1 value makes log_directory_changes() not call log_dir_items()
again;
2) Before returning with success (0), log_dir_items(), will log a dir
index range item covering a range from the last old dentry index
(stored in the variable 'last_old_dentry_offset') to the value of
'last_offset'. If 'last_offset' has a value of (u64)-1, then it means
if the log is persisted and replayed after a power failure, it will
cause deletion of all the directory entries that have an index number
between last_old_dentry_offset + 1 and (u64)-1;
3) We can end up returning from log_dir_items() with
ctx->last_dir_item_offset having a lower value than
inode->last_dir_index_offset, because the former is set to the current
key we are processing at process_dir_items_leaf(), and at the end of
log_directory_changes() we set inode->last_dir_index_offset to the
current value of ctx->last_dir_item_offset. So if for example a
deletion of a lower dir index key happened, we set
ctx->last_dir_item_offset to that index value, then if we return from
log_dir_items() because btrfs_search_slot() returned an error, we end up
returning without any error from log_dir_items() and then
log_directory_changes() sets inode->last_dir_index_offset to a lower
value than it had before.
This can result in unpredictable and unexpected behaviour when we
need to log again the directory in the same transaction, and can result
in ending up with a log tree leaf that has duplicated keys, as we do
batch insertions of dir index keys into a log tree.
Fix this by setting 'err' to the value of 'ret' in case
btrfs_search_slot() or btrfs_previous_item() returned an error. That will
result in falling back to a full transaction commit.
Reported-by: David Arendt <admin@prnet.org>
Link: https://lore.kernel.org/linux-btrfs/ae169fc6-f504-28f0-a098-6fa6a4dfb612@leemhuis.info/
Fixes:
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History
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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.