linux-kernel - Re: [PATCH v4 3/7] selftest/mm: Fix ksm_funtional

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Message-ID: <20250816140754.tgkn5kwf2i2oe7va@master>
Date: Sat, 16 Aug 2025 14:07:54 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Aboorva Devarajan <aboorvad@...ux.ibm.com>
Cc: akpm@...ux-foundation.org, Liam.Howlett@...cle.com,
	lorenzo.stoakes@...cle.com, shuah@...nel.org, pfalcato@...e.de,
	david@...hat.com, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
	npache@...hat.com, ryan.roberts@....com, dev.jain@....com,
	baohua@...nel.org, richard.weiyang@...il.com, linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	donettom@...ux.ibm.com, ritesh.list@...il.com
Subject: Re: [PATCH v4 3/7] selftest/mm: Fix ksm_funtional_test failures

On Sat, Aug 16, 2025 at 09:31:09AM +0530, Aboorva Devarajan wrote:
>From: Donet Tom <donettom@...ux.ibm.com>
>
>This patch fixed 2 issues.
>
>1) After fork() in test_prctl_fork, the child process uses the file
>descriptors from the parent process to read ksm_stat and
>ksm_merging_pages. This results in incorrect values being read (parent
>process ksm_stat and ksm_merging_pages will be read in child), causing
>the test to fail.
>
>This patch calls init_global_file_handles() in the child process to
>ensure that the current process's file descriptors are used to read
>ksm_stat and ksm_merging_pages.
>
>2) All tests currently call ksm_merge to trigger page merging.
>To ensure the system remains in a consistent state for subsequent
>tests, it is better to call ksm_unmerge during the test cleanup phase
>
>In the test_prctl_fork test, after a fork(), reading ksm_merging_pages
>in the child process returns a non-zero value because a previous test
>performed a merge, and the child's memory state is inherited from the
>parent.
>
>Although the child process calls ksm_unmerge, the ksm_merging_pages
>counter in the parent is reset to zero, while the child's counter
>remains unchanged. This discrepancy causes the test to fail.
>
>To avoid this issue, each test should call ksm_unmerge during cleanup
>to ensure the counter is reset and the system is in a clean state for
>subsequent tests.
>
>execv argument is an array of pointers to null-terminated strings.
>In this patch we also added NULL in the execv argument.
>
>Fixes: 6c47de3be3a0 ("selftest/mm: ksm_functional_tests: extend test case for ksm fork/exec")
>Co-developed-by: Aboorva Devarajan <aboorvad@...ux.ibm.com>
>Signed-off-by: Aboorva Devarajan <aboorvad@...ux.ibm.com>
>Signed-off-by: Donet Tom <donettom@...ux.ibm.com>

Reviewed-by: Wei Yang <richard.weiyang@...il.com>

-- 
Wei Yang
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