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bh=/k/DigVUZahp+YTSmfVTEyZ10bn5ZiBoZvjQJh0A0Ic=; b=RcTvy/8nIj5DOVdbNqsJBUqeYl m+fw/e78kf5y1dMfRYd/igfIJDRdc8kr5x4nfjaQg1fkikEl5kmPWlOrmnY6jITtrWlarSJZrNYDq krDpwnbJGpNrufJqyODKSjNVLyMI+VQ+Ur0fmiTKllKDIkrP9xkgkjyJq0C/4euxgGY0=; Received: from guillaum by bender.morinfr.org with local (Exim 4.98.2) (envelope-from ) id 1x2Zg3-00000002jwO-0eAH; Fri, 04 Sep 2026 21:34:19 +0200 Date: Fri, 4 Sep 2026 21:34:19 +0200 From: Guillaume Morin To: linux-mm@kvack.org Cc: leitao@debian.org, guillaume@morinfr.org, rppt@kernel.org Subject: [PATCH v4] selftests/mm: hugetlb_madv_vs_map: add underflow test Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: dstmx95edhx8rbbfm8hqr7bx3toregss X-Rspamd-Queue-Id: 6AD0A180009 X-HE-Tag: 1788550464-160184 X-HE-Meta: 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 FhXk5K6i Qycw7RSva3c3tuOyD+MFFAHm9vF61cvWI6Jbn/KMkfKEfjumxlFUTdWDVfMqfJrqIZUfSdQonIKieoT1uG52/VFnx8zlByOxxdtHuBn6vbewhe83H0jgg00adHg3XtJOOyK9/UJT7OG17oqrnQeQtwdiEGml6wqJXk8TL9nMO+P6Ud1fgxRqKCEfhch86ZiJ96RpiqzEezx4AmukR2j8hvpQgCe5RjouCtcZz/wS3x3v+VdTy/SKovrtmLZSxIUTcfSAmuTjFGk38F4BB4GsOVjjywT1s11T8rHbrEr2to/OlTg9nd9g+7P3B45AAXa1npWKMB2UuFtFDM7lDAbFUFwXaI24DRQ8ih24KUPckb3naelAkwz7eZSaoGJnfIKXP8PyhJurFJb3IsWbU6gmzPevhA6H0gwMOg5ea Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Add a test that checks for underflows when a parent unmaps the page first. Also check that when the child exits the reserve count is correct. Link: https://lore.kernel.org/all/alEJkwn5VlTTH_ZX@bender.morinfr.org/ Signed-off-by: Guillaume Morin Cc: Mike Rapoport --- v4: address Mike's comments v3: address Mike's comments v2: refactor tests into 2 functions .../testing/selftests/mm/hugepage_settings.c | 9 ++ .../testing/selftests/mm/hugepage_settings.h | 1 + .../selftests/mm/hugetlb_madv_vs_map.c | 145 +++++++++++++++--- 3 files changed, 134 insertions(+), 21 deletions(-) diff --git a/tools/testing/selftests/mm/hugepage_settings.c b/tools/testing/selftests/mm/hugepage_settings.c index d7917dce3aba..584054736ce9 100644 --- a/tools/testing/selftests/mm/hugepage_settings.c +++ b/tools/testing/selftests/mm/hugepage_settings.c @@ -449,6 +449,15 @@ unsigned long hugetlb_free_pages(unsigned long size) return read_num(path); } +unsigned long hugetlb_nr_resv_pages(unsigned long size) +{ + char path[PATH_MAX]; + + hugetlb_sysfs_path(path, sizeof(path), size, "resv_hugepages"); + + return read_num(path); +} + static bool __hugetlb_setup(unsigned long size, unsigned long nr) { unsigned long free = hugetlb_free_pages(size); diff --git a/tools/testing/selftests/mm/hugepage_settings.h b/tools/testing/selftests/mm/hugepage_settings.h index 726c73c43c05..548e9d288d1d 100644 --- a/tools/testing/selftests/mm/hugepage_settings.h +++ b/tools/testing/selftests/mm/hugepage_settings.h @@ -98,6 +98,7 @@ unsigned long default_huge_page_size(void); unsigned long hugetlb_nr_pages(unsigned long size); void hugetlb_set_nr_pages(unsigned long size, unsigned long nr); unsigned long hugetlb_free_pages(unsigned long size); +unsigned long hugetlb_nr_resv_pages(unsigned long size); static inline void hugetlb_save_settings(void) { diff --git a/tools/testing/selftests/mm/hugetlb_madv_vs_map.c b/tools/testing/selftests/mm/hugetlb_madv_vs_map.c index f94549efcc6f..d89b2c27c2ae 100644 --- a/tools/testing/selftests/mm/hugetlb_madv_vs_map.c +++ b/tools/testing/selftests/mm/hugetlb_madv_vs_map.c @@ -3,25 +3,16 @@ * A test case that must run on a system with one and only one huge page available. * # echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages * - * During setup, the test allocates the only available page, and starts three threads: - * - thread1: - * * madvise(MADV_DONTNEED) on the allocated huge page - * - thread 2: - * * Write to the allocated huge page - * - thread 3: - * * Try to allocated an extra huge page (which must not available) - * - * The test fails if thread3 is able to allocate a page. - * - * Touching the first page after thread3's allocation will raise a SIGBUS - * * Author: Breno Leitao */ +#include #include +#include #include #include #include #include +#include #include #include "vm_util.h" @@ -74,7 +65,21 @@ void *map_extra(void *unused) return NULL; } -int main(void) +/* During setup in main, the only available page was allocated. This test then + * starts three threads: + * + * - thread1: + * * madvise(MADV_DONTNEED) on the allocated huge page + * - thread 2: + * * Write to the allocated huge page + * - thread 3: + * * Try to allocated an extra huge page (which must not available) + * + * The test fails if thread3 is able to allocate a page. + * + * Touching the first page after thread3's allocation will raise a SIGBUS + */ +void test_madv_vs_map(void) { pthread_t thread1, thread2, thread3; void *ret; @@ -85,13 +90,6 @@ int main(void) */ int max = 10; - ksft_print_header(); - ksft_set_plan(1); - - if (!hugetlb_setup_default_exact(1)) - ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n", - hugetlb_free_default_pages()); - mmap_size = default_huge_page_size(); while (max--) { @@ -100,7 +98,7 @@ int main(void) -1, 0); if ((unsigned long)huge_ptr == -1) - ksft_exit_fail_msg("Failed to allocate huge page\n"); + ksft_exit_fail_perror("Failed to allocate huge page\n"); pthread_create(&thread1, NULL, madv, NULL); pthread_create(&thread2, NULL, touch, NULL); @@ -120,5 +118,110 @@ int main(void) } ksft_test_result_pass("No unexpected huge page allocations\n"); +} + +/* We create a child process, then unmap the page in the parent while the child + * waits and verify that there is no underflow of the reserved count. We also + * verify that after the child exits, the reserved count is properly restored. + */ +void test_underflow(void) +{ + pid_t pid; + int pipe_fds[2]; + unsigned long nr_reserved = 0; + + huge_ptr = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0); + + if ((unsigned long)huge_ptr == -1) + ksft_exit_fail_perror("Failed to allocate huge page\n"); + + nr_reserved = hugetlb_nr_resv_pages(default_huge_page_size()); + if (nr_reserved != 1) + ksft_exit_fail_msg("Unexpected number of reserved pages: %lu, expected 1\n", + nr_reserved); + + /* Force the fault to ensure the reservation is consumed */ + *huge_ptr = 0; + nr_reserved = hugetlb_nr_resv_pages(default_huge_page_size()); + if (nr_reserved != 0) + ksft_exit_fail_msg("Unexpected number of reserved pages: %lu, expected 0\n", + nr_reserved); + + if (pipe(pipe_fds) != 0) + ksft_exit_fail_perror("pipe failed"); + + pid = fork(); + if (pid < 0) + ksft_exit_fail_perror("fork failed"); + + if (pid == 0) { + /* Child: Simply wait for the parent */ + char b; + + close(pipe_fds[1]); + if (read(pipe_fds[0], &b, 1) < 0) + ksft_perror("child read failed"); + /* Let the parent do the cleanup */ + _exit(0); + } + + /* Parent */ + close(pipe_fds[0]); + + /* First unmap, this will close the vma */ + if (munmap(huge_ptr, mmap_size) != 0) { + ksft_perror("munmap failed"); + goto err_cleanup; + } + + nr_reserved = hugetlb_nr_resv_pages(default_huge_page_size()); + if (nr_reserved == 0) { + ksft_test_result_pass("Underflow not present!\n"); + } else { + ksft_test_result_fail("Unexpected HugePages_Rsvd=%ld after munmap, should be 0\n", + nr_reserved); + goto err_cleanup; + } + /* Make the child exit, this should restore HugePages_Rsvd to 0 */ + if (write(pipe_fds[1], &nr_reserved, 1) < 0) { + /* If write failed, the child is likely already gone */ + ksft_exit_fail_perror("write failed"); + } + close(pipe_fds[1]); + if (waitpid(pid, NULL, 0) <= 0) { + ksft_exit_fail_msg("waitpid failed\n"); + } + + nr_reserved = hugetlb_nr_resv_pages(default_huge_page_size()); + if (nr_reserved == 0) { + ksft_test_result_pass("After the child dies, HugePages_Rsvd is properly set to 0\n"); + } else { + ksft_exit_fail_msg("Unexpected HugePages_Rsvd=%ld after the child termination munmap, should be 0\n", nr_reserved); + } + return; + +err_cleanup: + if (write(pipe_fds[1], &nr_reserved, 1) < 0) { + ksft_exit_fail_perror("write failed"); + } + if (waitpid(pid, NULL, 0) <= 0) { + ksft_exit_fail_perror("waitpid failed"); + } + ksft_exit_fail(); +} + +int main(void) +{ + ksft_print_header(); + ksft_set_plan(3); + + if (!hugetlb_setup_default_exact(1)) + ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n", + hugetlb_free_default_pages()); + + test_madv_vs_map(); + test_underflow(); + ksft_finished(); } -- 2.39.1 -- Guillaume Morin