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3f7a79d05c
When the MB_CHECK_ASSERT macro is enabled, an assertion failure can
occur in __mb_check_buddy when checking preallocated blocks (pa) in
a block group:
Assertion failure in mb_free_blocks() : "groupnr == e4b->bd_group"
This happens when a pa at the very end of a block group (e.g.,
pa_pstart=32765, pa_len=3 in a group of 32768 blocks) becomes
exhausted - its pa_pstart is advanced by pa_len to 32768, which
lies in the next block group. If this exhausted pa (with pa_len == 0)
is still in the bb_prealloc_list during the buddy check, the assertion
incorrectly flags it as belonging to the wrong group. A possible
sequence is as follows:
ext4_mb_new_blocks
ext4_mb_release_context
pa->pa_pstart += EXT4_C2B(sbi, ac->ac_b_ex.fe_len)
pa->pa_len -= ac->ac_b_ex.fe_len
__mb_check_buddy
for each pa in group
ext4_get_group_no_and_offset
MB_CHECK_ASSERT(groupnr == e4b->bd_group)
To fix this, we modify the check to skip block group validation for
exhausted preallocations (where pa_len == 0). Such entries are in a
transitional state and will be removed from the list soon, so they
should not trigger an assertion. This change prevents the false
positive while maintaining the integrity of the checks for active
allocations.
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 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.