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bh=kErT8w6ahMkgn4ka2w1WDE1w6vOoaaaekm8TOYJyiFI=; b=HjvMyMk1d+FFUuheBWhHNMIzla H3qqPBpaOaHdlm1mlVXzvyyWSE27WjY/TrabylkMQoEswQhkxmB/pSU+t5pgQeMi4ioFzn06RVZ9F q2mxh0hBAbYHlHQhlfZybYR92z0fJt4z5cHqiiSBe9zqqc8Qgfhe4BSIEVQgGKaRq0Uk=; Received: from guillaum by bender.morinfr.org with local (Exim 4.98.2) (envelope-from ) id 1wzxZz-00000001E9O-2QOS; Fri, 28 Aug 2026 16:29:15 +0200 Date: Fri, 28 Aug 2026 16:29:15 +0200 From: Guillaume Morin To: linux-mm@kvack.org Cc: guillaume@morinfr.org, leitao@debian.org, rppt@kernel.org Subject: [PATCH v2] 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-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 2731940002 X-Stat-Signature: 7qfmuj4nk11aky8hdtksda3uni7467mi X-HE-Tag: 1787927359-450473 X-HE-Meta: U2FsdGVkX1+ZHyHteFMv/p1K5sYqdmFrOvODd9felpKHAUlOrnxzmA5w+hXKmuVc4MGKQ/mmOssAtWpfW/YIHrFgsB6Y8O7SfhpyXhOTqpzQCYOv+npGyuFkql7FNk2aXVOJTwsZd8J2K7hYHWNjDRVWS3Mybs5OQJNVjB96VfuBtNERdDW7naLl/b+hDi8Ft8Tc+gSTdTQkzATdPnWYI1O2c7Xat+E1tqfKI3nexHs/NxX0mo5wGrh0R2ofAVeWiZT0dhM578JACWhS5N1WsGxDsWY8v+/hcCo5EnWF5tz9nk+zGD2ALTRD1VCG7g9PUagjsdjQhSeIFcBx6EWKlQ85//xpvJWHnhmUrM/4zwDWbs1mC+DNEDhJa/zF3rTeMIWMjInR4HqssSvwzAjpxjD4/Htq59dQfQuzFPup/B2TG8ADTBPw7xLA9NpLEIzOBGX5OB95iHcJTdm+qO4yPIUMh3TOuRgSgQQFf2/QMQMbKQz9jK/r7dtTPr9swCE3GeQqcuOaK02xiOESBxrghVUaDdq3Ncz+2UfMJafkp4ZxmEly8Jx3+TYokhNnUOhWtt0R6IAONcNmrnn3CbNgUIAkNYK/ea4sFj5y1Wf8PUzG72hrKhTarMd0iAKBAk+BFsbfxMcnmRbWZ0Oc+mWP4d+LDQWIwUrmwhAa5wx5xZVWyEsKLvvif1ssjMt3oSK0sPchw3arq/eenFddnhpoH+GfTLSLuDQg1CQve62h5AV16HKwFkdxo+4vg1yjhnMu2r1EMJMSoAZinKuwrPESM/47HL8DlUUsz3H+4KVWDGm9tyECOpOUi44vmNWBttYF4fXaShaR1TP6VBbTxI5ZklzXiM3RcfWilDGa2yt7gCExtCzCEWJ+psKHitQqJ4crdQKz2LpHc4EwNxXqvSPp62TwoqLMtPVSNPGVmB3NFKCuYNtNxeEYQL+y4dhOxkYyRAXgEqwkwl84sta+gNN vVMLdV6g 0P3rtN3YTSTk0CB9SMaKjMWDmyUIMDXD+GUuPEjby+QG/BxZlzM3nGrkGgP25w0f47W2g9cvf3Gh/ycuAWFVIvTnuPAXSssP2AUfbqHJ0MepZFjqonsvKC3hmxHD2WtVWntYkgud6fuLXSFqylqEad0Y2+Ku/xMc+kohbCMNXkYjWa6YFvROIu72Ea0ZLE49evSG+t/I4HdwHMcLtw3pT6s/axfsS9NiiXELxWEdzNvUQPxxzX4uY7WtXgs/VxR1DGXrnJmhzGEvBugKS9u1koWuoVpNnT7xRfQ2VHltBFpgp4YivbZ+EQzpDBrsCNUc6lTJyz0q9Q1iLZFiSNFb6h4kimarF/t9Fg8R1iyaWIY5DC54wDDMRZwZTwCe8xhAIapdZ1XD7hYn9A959sOs0vvvbrsbX5C1w47vq 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 --- v2: factor out tests .../testing/selftests/mm/hugepage_settings.c | 9 ++ .../testing/selftests/mm/hugepage_settings.h | 1 + .../selftests/mm/hugetlb_madv_vs_map.c | 107 ++++++++++++++++-- 3 files changed, 109 insertions(+), 8 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..d1f568fed4aa 100644 --- a/tools/testing/selftests/mm/hugetlb_madv_vs_map.c +++ b/tools/testing/selftests/mm/hugetlb_madv_vs_map.c @@ -15,13 +15,20 @@ * * Touching the first page after thread3's allocation will raise a SIGBUS * + * We setup a 2nd test where 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. + * * Author: Breno Leitao */ +#include #include +#include #include #include #include #include +#include #include #include "vm_util.h" @@ -74,7 +81,7 @@ void *map_extra(void *unused) return NULL; } -int main(void) +void test_madv_vs_map(void) { pthread_t thread1, thread2, thread3; void *ret; @@ -85,13 +92,6 @@ 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--) { @@ -120,5 +120,96 @@ int main(void) } ksft_test_result_pass("No unexpected huge page allocations\n"); +} + +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_msg("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_msg("pipe failed"); + + pid = fork(); + if (pid < 0) + ksft_exit_fail_msg("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_exit_fail_msg("child read failed"); + return; + } + + /* Parent */ + close(pipe_fds[0]); + + /* First unmap, this will close the vma */ + if (munmap(huge_ptr, mmap_size) != 0) { + kill(pid, SIGKILL); + ksft_exit_fail_msg("munmap failed"); + } + + nr_reserved = hugetlb_nr_resv_pages(default_huge_page_size()); + if (nr_reserved == ULONG_MAX) { + ksft_test_result_fail("After the munmap, HugePages_Rsvd underflowed!\n"); + } else if (nr_reserved == 0) { + ksft_test_result_pass("Underflow not present!\n"); + } else { + ksft_exit_fail_msg("Unexpected HugePages_Rsvd=%ld after munmap, should be 0 or -1. Repeat the test\n", + nr_reserved); + } + /* Make the child exit, this should restore HugePages_Rsvd to 0 */ + if (write(pipe_fds[1], &nr_reserved, 1) < 0) { + kill(pid, SIGKILL); + ksft_exit_fail_msg("write failed"); + } + close(pipe_fds[1]); + if (waitpid(pid, NULL, 0) <= 0) + ksft_exit_fail_msg("write failed"); + + 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 or -1. Repeat the test\n", + nr_reserved); + } +} + +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