The patch titled Subject: selftests/mm: compaction_test: fix bogus test success on Aarch64 has been added to the -mm mm-hotfixes-unstable branch. Its filename is selftests-mm-compaction_test-fix-bogus-test-success-on-aarch64.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Dev Jain dev.jain@arm.com Subject: selftests/mm: compaction_test: fix bogus test success on Aarch64 Date: Tue, 21 May 2024 13:13:56 +0530

Patch series "Fixes for compaction_test", v2.

The compaction_test memory selftest introduces fragmentation in memory and then tries to allocate as many hugepages as possible. This series addresses some problems.

On Aarch64, if nr_hugepages == 0, then the test trivially succeeds since compaction_index becomes 0, which is less than 3, due to no division by zero exception being raised. We fix that by checking for division by zero.

Secondly, correctly set the number of hugepages to zero before trying to set a large number of them.

Now, consider a situation in which, at the start of the test, a non-zero number of hugepages have been already set (while running the entire selftests/mm suite, or manually by the admin). The test operates on 80% of memory to avoid OOM-killer invocation, and because some memory is already blocked by hugepages, it would increase the chance of OOM-killing. Also, since mem_free used in check_compaction() is the value before we set nr_hugepages to zero, the chance that the compaction_index will be small is very high if the preset nr_hugepages was high, leading to a bogus test success.

This patch (of 3):

Currently, if at runtime we are not able to allocate a huge page, the test will trivially pass on Aarch64 due to no exception being raised on division by zero while computing compaction_index. Fix that by checking for nr_hugepages == 0. Anyways, in general, avoid a division by zero by exiting the program beforehand. While at it, fix a typo, and handle the case where the number of hugepages may overflow an integer.

Link: https://lkml.kernel.org/r/20240521074358.675031-1-dev.jain@arm.com Link: https://lkml.kernel.org/r/20240521074358.675031-2-dev.jain@arm.com Fixes: bd67d5c15cc1 ("Test compaction of mlocked memory") Signed-off-by: Dev Jain dev.jain@arm.com Cc: Anshuman Khandual anshuman.khandual@arm.com Cc: Shuah Khan shuah@kernel.org Cc: Sri Jayaramappa sjayaram@akamai.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

tools/testing/selftests/mm/compaction_test.c | 20 +++++++++++------ 1 file changed, 13 insertions(+), 7 deletions(-)

--- a/tools/testing/selftests/mm/compaction_test.c~selftests-mm-compaction_test-fix-bogus-test-success-on-aarch64 +++ a/tools/testing/selftests/mm/compaction_test.c @@ -82,12 +82,13 @@ int prereq(void) return -1; }

-int check_compaction(unsigned long mem_free, unsigned int hugepage_size) +int check_compaction(unsigned long mem_free, unsigned long hugepage_size) { + unsigned long nr_hugepages_ul; int fd, ret = -1; int compaction_index = 0; - char initial_nr_hugepages[10] = {0}; - char nr_hugepages[10] = {0}; + char initial_nr_hugepages[20] = {0}; + char nr_hugepages[20] = {0};

/* We want to test with 80% of available memory. Else, OOM killer comes in to play */ @@ -134,7 +135,12 @@ int check_compaction(unsigned long mem_f

/* We should have been able to request at least 1/3 rd of the memory in huge pages */ - compaction_index = mem_free/(atoi(nr_hugepages) * hugepage_size); + nr_hugepages_ul = strtoul(nr_hugepages, NULL, 10); + if (!nr_hugepages_ul) { + ksft_print_msg("ERROR: No memory is available as huge pages\n"); + goto close_fd; + } + compaction_index = mem_free/(nr_hugepages_ul * hugepage_size);

lseek(fd, 0, SEEK_SET);

@@ -145,11 +151,11 @@ int check_compaction(unsigned long mem_f goto close_fd; }

- ksft_print_msg("Number of huge pages allocated = %d\n", - atoi(nr_hugepages)); + ksft_print_msg("Number of huge pages allocated = %lu\n", + nr_hugepages_ul);

if (compaction_index > 3) { - ksft_print_msg("ERROR: Less that 1/%d of memory is available\n" + ksft_print_msg("ERROR: Less than 1/%d of memory is available\n" "as huge pages\n", compaction_index); goto close_fd; } _

Patches currently in -mm which might be from dev.jain@arm.com are

selftests-mm-compaction_test-fix-bogus-test-success-on-aarch64.patch selftests-mm-compaction_test-fix-incorrect-write-of-zero-to-nr_hugepages.patch selftests-mm-compaction_test-fix-bogus-test-success-and-reduce-probability-of-oom-killer-invocation.patch