Commit 01040964 authored by Dev Jain's avatar Dev Jain Committed by Andrew Morton
Browse files

selftests/mm: confirm VA exhaustion without reliance on correctness of mmap() 

Currently, VA exhaustion is being checked by passing a hint to mmap() and
expecting it to fail.

While populating the lower VA space, mmap() fails because we have 
exhausted the space.

Then, in validate_lower_address_hint(), because mmap() fails, we
confirm that we have indeed exhausted the space.  There is a circular
logic involved here.

Assume that there is a bug in mmap(), also assume that it exists
independent of whether you pass a hint address or not; that for some
reason it is not able to find a 1GB chunk.  My idea is to assert the
exhaustion against some other method.

This patch makes a stricter test by successful
write() calls from /proc/self/maps to a dump file, confirming that a free
chunk is indeed not available.

[dev.jain@arm.com: replace SZ_1GB with MAP_CHUNK_SIZE, tidy-up]
  Link: https://lkml.kernel.org/r/20240325042653.867055-1-dev.jain@arm.com
Link: https://lkml.kernel.org/r/20240321103522.516097-1-dev.jain@arm.com


Signed-off-by: default avatarDev Jain <dev.jain@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 42a346b4

tools/testing/selftests/mm/virtual_address_range.c

+66 −0
Original line number Diff line number Diff line
@@ -12,6 +12,8 @@ 
#include <errno.h>

#include <sys/mman.h>

#include <sys/time.h>

#include <fcntl.h>



#include "../kselftest.h"



/*
@@ -93,6 +95,66 @@ static int validate_lower_address_hint(void) 
	return 1;

}



static int validate_complete_va_space(void)

{

	unsigned long start_addr, end_addr, prev_end_addr;

	char line[400];

	char prot[6];

	FILE *file;

	int fd;



	fd = open("va_dump", O_CREAT | O_WRONLY, 0600);

	unlink("va_dump");

	if (fd < 0) {

		ksft_test_result_skip("cannot create or open dump file\n");

		ksft_finished();

	}



	file = fopen("/proc/self/maps", "r");

	if (file == NULL)

		ksft_exit_fail_msg("cannot open /proc/self/maps\n");



	prev_end_addr = 0;

	while (fgets(line, sizeof(line), file)) {

		unsigned long hop;



		if (sscanf(line, "%lx-%lx %s[rwxp-]",

			   &start_addr, &end_addr, prot) != 3)

			ksft_exit_fail_msg("cannot parse /proc/self/maps\n");



		/* end of userspace mappings; ignore vsyscall mapping */

		if (start_addr & (1UL << 63))

			return 0;



		/* /proc/self/maps must have gaps less than MAP_CHUNK_SIZE */

		if (start_addr - prev_end_addr >= MAP_CHUNK_SIZE)

			return 1;



		prev_end_addr = end_addr;



		if (prot[0] != 'r')

			continue;



		/*

		 * Confirm whether MAP_CHUNK_SIZE chunk can be found or not.

		 * If write succeeds, no need to check MAP_CHUNK_SIZE - 1

		 * addresses after that. If the address was not held by this

		 * process, write would fail with errno set to EFAULT.

		 * Anyways, if write returns anything apart from 1, exit the

		 * program since that would mean a bug in /proc/self/maps.

		 */

		hop = 0;

		while (start_addr + hop < end_addr) {

			if (write(fd, (void *)(start_addr + hop), 1) != 1)

				return 1;

			lseek(fd, 0, SEEK_SET);



			hop += MAP_CHUNK_SIZE;

		}

	}

	return 0;

}



int main(int argc, char *argv[])

{

	char *ptr[NR_CHUNKS_LOW];
@@ -133,6 +195,10 @@ int main(int argc, char *argv[]) 
		validate_addr(hptr[i], 1);

	}

	hchunks = i;

	if (validate_complete_va_space()) {

		ksft_test_result_fail("BUG in mmap() or /proc/self/maps\n");

		ksft_finished();

	}



	for (i = 0; i < lchunks; i++)

		munmap(ptr[i], MAP_CHUNK_SIZE);