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crash_exclude_mem_range seems to be a simple function but there have been multiple attempts to fix it, - commita2e9a95d21("kexec: Improve & fix crash_exclude_mem_range() to handle overlapping ranges") - commit6dff315972("crash_core: fix and simplify the logic of crash_exclude_mem_range()") So add a set of unit tests to verify the correctness of current implementation. Shall we change the function in the future, the unit tests can also help prevent any regression. For example, we may make the function smarter by allocating extra crash_mem range on demand thus there is no need for the caller to foresee any memory range split or address -ENOMEM failure. The testing strategy is to verify the correctness of base case. The base case is there is one to-be-excluded range A and one existing range B. Then we can exhaust all possibilities of the position of A regarding B. For example, here are two combinations, Case: A is completely inside B (causes split) Original: [----B----] Exclude: {--A--} Result: [B1] .. [B2] Case: A overlaps B's left part Original: [----B----] Exclude: {---A---} Result: [..B..] In theory we can prove the correctness by induction, - Base case: crash_exclude_mem_range is correct in the case where n=1 (n is the number of existing ranges). - Inductive step: If crash_exclude_mem_range is correct for n=k existing ranges, then the it's also correct for n=k+1 ranges. But for the sake of simplicity, simply use unit tests to cover the base case together with two regression tests. Note most of the exclude_single_range_test() code is generated by Google Gemini with some small tweaks. The function specification, function body and the exhausting test strategy are presented as prompts. [akpm@linux-foundation.org: export crash_exclude_mem_range() to modules, for kernel/crash_core_test.c] Link: https://lkml.kernel.org/r/20250904093855.1180154-2-coxu@redhat.com Signed-off-by: Coiby Xu <coxu@redhat.com> Assisted-by: Google Gemini Cc: Baoquan He <bhe@redhat.com> Cc: Borislav Betkov <bp@alien8.de> Cc: Dave Young <dyoung@redhat.com> Cc: fuqiang wang <fuqiang.wang@easystack.cn> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Thomas Gleinxer <tglx@linutronix.de> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.