Re: [PATCH] selftest: mm: Test if hugepage does not get leaked during __bio_release_pages()

Donet Tom
2024-05-25T15:41:15Z

On 5/24/24 23:43, Muhammad Usama Anjum wrote:
> Thank you for submitting a patch.
>
> On 5/22/24 11:39 PM, Donet Tom wrote:
>> Commit 1b151e2435fc ("block: Remove special-casing of compound
>> pages") caused a change in behaviour when releasing the pages
>> if the buffer does not start at the beginning of the page. This
>> was because the calculation of the number of pages to release
>> was incorrect.
>> This was fixed by commit 38b43539d64b ("block: Fix page refcounts
>> for unaligned buffers in __bio_release_pages()").
>>
>> We pin the user buffer during direct I/O writes. If this buffer is a
>> hugepage, bio_release_page() will unpin it and decrement all references
>> and pin counts at ->bi_end_io. However, if any references to the hugepage
>> remain post-I/O, the hugepage will not be freed upon unmap, leading
>> to a memory leak.
>>
>> This patch verifies that a hugepage, used as a user buffer for DIO
>> operations, is correctly freed upon unmapping, regardless of whether
>> the offsets are aligned or unaligned w.r.t page boundary.
>>
>> Test Result Fail Scenario (Without the fix)
>> --------------------------------------------------------
>> []# ./hugetlb_dio
>> TAP version 13
>> 1..4
>> No. Free pages before allocation : 7
>> No. Free pages after munmap : 7
>> ok 1 : Huge pages freed successfully !
>> No. Free pages before allocation : 7
>> No. Free pages after munmap : 7
>> ok 2 : Huge pages freed successfully !
>> No. Free pages before allocation : 7
>> No. Free pages after munmap : 7
>> ok 3 : Huge pages freed successfully !
>> No. Free pages before allocation : 7
>> No. Free pages after munmap : 6
>> not ok 4 : Huge pages not freed!
>> Totals: pass:3 fail:1 xfail:0 xpass:0 skip:0 error:0
>>
>> Test Result PASS Scenario (With the fix)
>> ---------------------------------------------------------
>> []#./hugetlb_dio
>> TAP version 13
>> 1..4
>> No. Free pages before allocation : 7
>> No. Free pages after munmap : 7
>> ok 1 : Huge pages freed successfully !
>> No. Free pages before allocation : 7
>> No. Free pages after munmap : 7
>> ok 2 : Huge pages freed successfully !
>> No. Free pages before allocation : 7
>> No. Free pages after munmap : 7
>> ok 3 : Huge pages freed successfully !
>> No. Free pages before allocation : 7
>> No. Free pages after munmap : 7
>> ok 4 : Huge pages freed successfully !
>> Totals: pass:4 fail:0 xfail:0 xpass:0 skip:0 error:0
>>
>> Signed-off-by: Donet Tom <donettom@linux.ibm.com>
>> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
>> ---
>> tools/testing/selftests/mm/Makefile | 1 +
>> tools/testing/selftests/mm/hugetlb_dio.c | 118 +++++++++++++++++++++++
> Add this test to vm_runtest.sh as all the tests are run from this script in
> CIs.
>
>> 2 files changed, 119 insertions(+)
>> create mode 100644 tools/testing/selftests/mm/hugetlb_dio.c
>>
>> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
>> index eb5f39a2668b..87d8130b3376 100644
>> --- a/tools/testing/selftests/mm/Makefile
>> +++ b/tools/testing/selftests/mm/Makefile
>> @@ -71,6 +71,7 @@ TEST_GEN_FILES += ksm_functional_tests
>> TEST_GEN_FILES += mdwe_test
>> TEST_GEN_FILES += hugetlb_fault_after_madv
>> TEST_GEN_FILES += hugetlb_madv_vs_map
>> +TEST_GEN_FILES += hugetlb_dio
>>
>> ifneq ($(ARCH),arm64)
>> TEST_GEN_FILES += soft-dirty
>> diff --git a/tools/testing/selftests/mm/hugetlb_dio.c b/tools/testing/selftests/mm/hugetlb_dio.c
>> new file mode 100644
>> index 000000000000..6f6587c7913c
>> --- /dev/null
>> +++ b/tools/testing/selftests/mm/hugetlb_dio.c
>> @@ -0,0 +1,118 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * This program tests for hugepage leaks after DIO writes to a file using a
>> + * hugepage as the user buffer. During DIO, the user buffer is pinned and
>> + * should be properly unpinned upon completion. This patch verifies that the
>> + * kernel correctly unpins the buffer at DIO completion for both aligned and
>> + * unaligned user buffer offsets (w.r.t page boundary), ensuring the hugepage
>> + * is freed upon unmapping.
>> + */
>> +
>> +#define _GNU_SOURCE
>> +#include <stdio.h>
>> +#include <sys/stat.h>
>> +#include <stdlib.h>
>> +#include <fcntl.h>
>> +#include <stdint.h>
>> +#include <unistd.h>
>> +#include <string.h>
>> +#include <sys/mman.h>
>> +#include "vm_util.h"
>> +#include "../kselftest.h"
>> +
>> +void run_dio_using_hugetlb(unsigned int start_off, unsigned int end_off)
>> +{
>> + int fd;
>> + char *buffer = NULL;
>> + char *orig_buffer = NULL;
>> + size_t h_pagesize = 0;
>> + size_t writesize;
>> + int free_hpage_b = 0;
>> + int free_hpage_a = 0;
>> +
>> + writesize = end_off - start_off;
>> +
>> + /* Get the default huge page size */
>> + h_pagesize = default_huge_page_size();
>> + if (!h_pagesize)
>> + ksft_exit_fail_msg("Unable to determine huge page size\n");
>> +
>> + /* Open the file to DIO */
>> + fd = open("/tmp", O_TMPFILE | O_RDWR | O_DIRECT);
>> + if (fd < 0)
>> + ksft_exit_fail_msg("Error opening file");
> Use ksft_exit_fail_perror to print the info about the error
>> +
>> + /* Get the free huge pages before allocation */
>> + free_hpage_b = get_free_hugepages();
>> + if (free_hpage_b == 0) {
>> + close(fd);
>> + ksft_exit_skip("No free hugepage, exiting!\n");
>> + }
>> +
>> + /* Allocate a hugetlb page */
>> + orig_buffer = mmap(NULL, h_pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE
>> + | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
> Better align the arguments. Put all flags in one line instead of slitting
> like this
>
>> + if (orig_buffer == MAP_FAILED) {
>> + close(fd);
>> + ksft_exit_fail_msg("Error mapping memory");
> nit: "\n" is missing from here.
>
>> + }
>> + buffer = orig_buffer;
>> + buffer += start_off;
>> +
>> + memset(buffer, 'A', writesize);
>> +
>> + /* Write the buffer to the file */
>> + if (write(fd, buffer, writesize) != (writesize)) {
>> + munmap(orig_buffer, h_pagesize);
>> + close(fd);
>> + ksft_exit_fail_msg("Error writing to file");
>> + }
>> +
>> + /* unmap the huge page */
>> + munmap(orig_buffer, h_pagesize);
>> + close(fd);
>> +
>> + /* Get the free huge pages after unmap*/
>> + free_hpage_a = get_free_hugepages();
>> +
>> + /*
>> + * If the no. of free hugepages before allocation and after unmap does
>> + * not match - that means there could still be a page which is pinned.
>> + */
>> + if (free_hpage_a != free_hpage_b) {
>> + printf("No. Free pages before allocation : %d\n", free_hpage_b);
> Use ksft_print_msg instead
>
>> + printf("No. Free pages after munmap : %d\n", free_hpage_a);
>> + ksft_test_result_fail(": Huge pages not freed!\n");
>> + } else {
>> + printf("No. Free pages before allocation : %d\n", free_hpage_b);
>> + printf("No. Free pages after munmap : %d\n", free_hpage_a);
>> + ksft_test_result_pass(": Huge pages freed successfully !\n");
>> + }
>> +}
>> +
>> +int main(void)
>> +{
>> + size_t pagesize = 0;
>> +
>> + ksft_print_header();
>> + ksft_set_plan(4);
>> +
>> + /* Get base page size */
>> + pagesize = psize();
>> +
>> + /* start and end is aligned to pagesize */
>> + run_dio_using_hugetlb(0, (pagesize * 3));
>> +
>> + /* start is aligned but end is not aligned */
>> + run_dio_using_hugetlb(0, (pagesize * 3) - (pagesize / 2));
>> +
>> + /* start is unaligned and end is aligned */
>> + run_dio_using_hugetlb(pagesize / 2, (pagesize * 3));
>> +
>> + /* both start and end are unaligned */
>> + run_dio_using_hugetlb(pagesize / 2, (pagesize * 3) + (pagesize / 2));
>> +
>> + ksft_finished();
> ksft_finished() never returns. Remove the following line.

Thank you for all your suggestions.  I will make all the changes and send V2.

Thanks
Donet

>> + return 0;
>> +}
>> +