Re: [PATCH 2/6] selftest/mm: Fix ksm_funtional_test failures

[donettom <donettom@linux.ibm.com>]

On Mon, Jun 16, 2025 at 01:04:40PM -0400, Liam R. Howlett wrote:
> * Aboorva Devarajan <aboorvad@linux.ibm.com> [250616 12:07]:
> > From: Donet Tom <donettom@linux.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: ?

Sorry I missed it. We will add and send a new version.

> 
> > Signed-off-by: Donet Tom <donettom@linux.ibm.com>
> > Signed-off-by: Aboorva Devarajan <aboorvad@linux.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
> > 
> >