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f56ee9af23
[ Upstream commit d4bf15a7ce172d186d400d606adf4f34a59130d6 ]
I recently found a case where de->name_len is 0 in f2fs_fill_dentries()
easily reproduced, and finally set the fsck flag.
Thread A Thread B
- f2fs_readdir
- f2fs_read_inline_dir
- ctx->pos = d.max
- f2fs_add_dentry
- f2fs_add_inline_entry
- do_convert_inline_dir
- f2fs_add_regular_entry
- f2fs_readdir
- f2fs_fill_dentries
- set_sbi_flag(sbi, SBI_NEED_FSCK)
Process A opens the folder, and has been reading without closing it.
During this period, Process B created a file under the folder (occupying
multiple f2fs_dir_entry, exceeding the d.max of the inline dir). After
creation, process A uses the d.max of inline dir to read it again, and
it will read that de->name_len is 0.
And Chao pointed out that w/o inline conversion, the race condition still
can happen as below:
dir_entry1: A
dir_entry2: B
dir_entry3: C
free slot: _
ctx->pos: ^
Thread A is traversing directory,
ctx-pos moves to below position after readdir() by thread A:
AAAABBBB___
^
Then thread B delete dir_entry2, and create dir_entry3.
Thread A calls readdir() to lookup dirents starting from middle
of new dirent slots as below:
AAAACCCCCC_
^
In these scenarios, the file system is not damaged, and it's hard to
avoid it. But we can bypass tagging FSCK flag if:
a) bit_pos (:= ctx->pos % d->max) is non-zero and
b) before bit_pos moves to first valid dir_entry.
Fixes:
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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.