linux-kernel - Re: [PATCH 2/6] selftest/mm: Fix ksm_funtional

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Message-ID: <5xw6iujjihdqy3sssmgo7z7rghsi3jgusc3kap7w7gbowisyc2@gfq633qx4bra>
Date: Mon, 16 Jun 2025 13:04:40 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Aboorva Devarajan <aboorvad@...ux.ibm.com>
Cc: akpm@...ux-foundation.org, 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, 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 2/6] selftest/mm: Fix ksm_funtional_test failures

* Aboorva Devarajan <aboorvad@...ux.ibm.com> [250616 12:07]:
> 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_merge_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.
> 

Fixes: ?

> Signed-off-by: Donet Tom <donettom@...ux.ibm.com>
> Signed-off-by: Aboorva Devarajan <aboorvad@...ux.ibm.com>
> ---
>  tools/testing/selftests/mm/ksm_functional_tests.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index b61803e36d1c..d7d3c22c077a 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -46,6 +46,8 @@ static int ksm_use_zero_pages_fd;
>  static int pagemap_fd;
>  static size_t pagesize;
>  
> +static void init_global_file_handles(void);
> +
>  static bool range_maps_duplicates(char *addr, unsigned long size)
>  {
>  	unsigned long offs_a, offs_b, pfn_a, pfn_b;
> @@ -274,6 +276,7 @@ static void test_unmerge(void)
>  	ksft_test_result(!range_maps_duplicates(map, size),
>  			 "Pages were unmerged\n");
>  unmap:
> +	ksm_unmerge();
>  	munmap(map, size);
>  }
>  
> @@ -338,6 +341,7 @@ static void test_unmerge_zero_pages(void)
>  	ksft_test_result(!range_maps_duplicates(map, size),
>  			"KSM zero pages were unmerged\n");
>  unmap:
> +	ksm_unmerge();
>  	munmap(map, size);
>  }
>  
> @@ -366,6 +370,7 @@ static void test_unmerge_discarded(void)
>  	ksft_test_result(!range_maps_duplicates(map, size),
>  			 "Pages were unmerged\n");
>  unmap:
> +	ksm_unmerge();
>  	munmap(map, size);
>  }
>  
> @@ -428,6 +433,7 @@ static void test_unmerge_uffd_wp(void)
>  close_uffd:
>  	close(uffd);
>  unmap:
> +	ksm_unmerge();
>  	munmap(map, size);
>  }
>  #endif
> @@ -491,6 +497,7 @@ static int test_child_ksm(void)
>  	else if (map == MAP_MERGE_SKIP)
>  		return -3;
>  
> +	ksm_unmerge();
>  	munmap(map, size);
>  	return 0;
>  }
> @@ -524,6 +531,7 @@ static void test_prctl_fork(void)
>  
>  	child_pid = fork();
>  	if (!child_pid) {
> +		init_global_file_handles();
>  		exit(test_child_ksm());
>  	} else if (child_pid < 0) {
>  		ksft_test_result_fail("fork() failed\n");
> @@ -620,6 +628,7 @@ static void test_prctl_unmerge(void)
>  	ksft_test_result(!range_maps_duplicates(map, size),
>  			 "Pages were unmerged\n");
>  unmap:
> +	ksm_unmerge();
>  	munmap(map, size);
>  }
>  
> @@ -653,6 +662,7 @@ static void test_prot_none(void)
>  	ksft_test_result(!range_maps_duplicates(map, size),
>  			 "Pages were unmerged\n");
>  unmap:
> +	ksm_unmerge();
>  	munmap(map, size);
>  }
>  
> -- 
> 2.43.5
> 
>