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94a0333b92
A concurrent file creation and little writing could unexpectedly return -ENOSPC error since there is a race window that the allocator could get the wrong agf->agf_longest. Write file process steps: 1) Find the entry that best meets the conditions, then calculate the start address and length of the remaining part of the entry after allocation. 2) Delete this entry and update the -current- agf->agf_longest. 3) Insert the remaining unused parts of this entry based on the calculations in 1), and update the agf->agf_longest again if necessary. Create file process steps: 1) Check whether there are free inodes in the inode chunk. 2) If there is no free inode, check whether there has space for creating inode chunks, perform the no-lock judgment first. 3) If the judgment succeeds, the judgment is performed again with agf lock held. Otherwire, an error is returned directly. If the write process is in step 2) but not go to 3) yet, the create file process goes to 2) at this time, it may be mistaken for no space, resulting in the file system still has space but the file creation fails. We have sent two different commits to the community in order to fix this problem[1][2]. Unfortunately, both solutions have flaws. In [2], I discussed with Dave and Darrick, realized that a better solution to this problem requires the "last cnt record tracking" to be ripped out of the generic btree code. And surprisingly, Dave directly provided his fix code. This patch includes appropriate modifications based on his tmp-code to address this issue. The entire fix can be roughly divided into two parts: 1) Delete the code related to lastrec-update in the generic btree code. 2) Place the process of updating longest freespace with cntbt separately to the end of the cntbt modifications. Move the cursor to the rightmost firstly, and update the longest free extent based on the record. Note that we can not update the longest with xfs_alloc_get_rec() after find the longest record, as xfs_verify_agbno() may not pass because pag->block_count is updated on the outside. Therefore, use xfs_btree_get_rec() as a replacement. [1] https://lore.kernel.org/all/20240419061848.1032366-2-yebin10@huawei.com [2] https://lore.kernel.org/all/20240604071121.3981686-1-wozizhi@huawei.com Reported by: Ye Bin <yebin10@huawei.com> Signed-off-by: Zizhi Wo <wozizhi@huawei.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Chandan Babu R <chandanbabu@kernel.org> |
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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 reStructuredText 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.