Commit 5bbc2b78 authored by Zi Yan's avatar Zi Yan Committed by Andrew Morton
Browse files

selftests/mm: fix FORCE_READ to read input value correctly 

FORCE_READ() converts input value x to its pointer type then reads from
address x.  This is wrong.  If x is a non-pointer, it would be caught it
easily.  But all FORCE_READ() callers are trying to read from a pointer
and FORCE_READ() basically reads a pointer to a pointer instead of the
original typed pointer.  Almost no access violation was found, except the
one from split_huge_page_test.

Fix it by implementing a simplified READ_ONCE() instead.

Link: https://lkml.kernel.org/r/20250805175140.241656-1-ziy@nvidia.com


Fixes: 3f6bfd47 ("selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));"")
Signed-off-by: default avatarZi Yan <ziy@nvidia.com>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarwang lian <lianux.mm@gmail.com>
Reviewed-by: default avatarWei Yang <richard.weiyang@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 9614d8be

tools/testing/selftests/mm/cow.c

+2 −2
Original line number Diff line number Diff line
@@ -1554,8 +1554,8 @@ static void run_with_zeropage(non_anon_test_fn fn, const char *desc) 
	}



	/* Read from the page to populate the shared zeropage. */

	FORCE_READ(mem);

	FORCE_READ(smem);

	FORCE_READ(*mem);

	FORCE_READ(*smem);



	fn(mem, smem, pagesize);

munmap:

tools/testing/selftests/mm/guard-regions.c

+1 −1
Original line number Diff line number Diff line
@@ -145,7 +145,7 @@ static bool try_access_buf(char *ptr, bool write) 
		if (write)

			*ptr = 'x';

		else

			FORCE_READ(ptr);

			FORCE_READ(*ptr);

	}



	signal_jump_set = false;

tools/testing/selftests/mm/hugetlb-madvise.c

+3 −1
Original line number Diff line number Diff line
@@ -50,8 +50,10 @@ void read_fault_pages(void *addr, unsigned long nr_pages) 
	unsigned long i;



	for (i = 0; i < nr_pages; i++) {

		unsigned long *addr2 =

			((unsigned long *)(addr + (i * huge_page_size)));

		/* Prevent the compiler from optimizing out the entire loop: */

		FORCE_READ(((unsigned long *)(addr + (i * huge_page_size))));

		FORCE_READ(*addr2);

	}

}

tools/testing/selftests/mm/migration.c

+1 −1
Original line number Diff line number Diff line
@@ -110,7 +110,7 @@ void *access_mem(void *ptr) 
		 * the memory access actually happens and prevents the compiler

		 * from optimizing away this entire loop.

		 */

		FORCE_READ((uint64_t *)ptr);

		FORCE_READ(*(uint64_t *)ptr);

	}



	return NULL;

tools/testing/selftests/mm/pagemap_ioctl.c

+1 −1
Original line number Diff line number Diff line
@@ -1525,7 +1525,7 @@ void zeropfn_tests(void) 


	ret = madvise(mem, hpage_size, MADV_HUGEPAGE);

	if (!ret) {

		FORCE_READ(mem);

		FORCE_READ(*mem);



		ret = pagemap_ioctl(mem, hpage_size, &vec, 1, 0,

				    0, PAGE_IS_PFNZERO, 0, 0, PAGE_IS_PFNZERO);