Re: [PATCH] tools/testing/selftests/vm/mlock2-tests: fix mlock2 false-negative errors

[Michal Hocko <mhocko@kernel.org>]

On Mon 23-03-20 11:41:59, Rafael Aquini wrote:
> On Mon, Mar 23, 2020 at 04:12:56PM +0100, Michal Hocko wrote:
> > On Mon 23-03-20 11:02:59, Rafael Aquini wrote:
[...]
> > > The selftest also checks the kernel visible effect, via
> > > /proc/kpageflags, and that's where it fails after 9c4e6b1a7027f.
> > 
> > I really fail to see your point. Even if you are right that the self
> > test is somehow evaluating the kernel implementation which I am not sure
> > is the scope of the selft thest but anyway. The mere fact that the
> > kernel test fails on a perfectly valid change should just suggest that
> > the test is leading to false positives and therefore should be fixed.
> > Your proposed fix is simply suboptimal because it relies on yet another
> > side effect which might change anytime in the future and still lead to a
> > correctly behaving kernel. See my point?
> >
> 
> OK, I concede your point on the bogusness of checking the page flags in
> this particular test and expect certain valuse there, given that no other 
> selftest seems to be doing that level of inner kenrel detail scrutiny.
> 
> I'll repost this fix suggestion getting rif of those related
> checkpoints.

Here is what I have after I had to context switch to something else
before finishing it. Feel free to reuse if you feel like. It is likely
to not even compile.

diff --git a/tools/testing/selftests/vm/mlock2-tests.c b/tools/testing/selftests/vm/mlock2-tests.c
index 637b6d0ac0d0..9fb1638a4d33 100644
--- a/tools/testing/selftests/vm/mlock2-tests.c
+++ b/tools/testing/selftests/vm/mlock2-tests.c
@@ -67,59 +67,6 @@ static int get_vm_area(unsigned long addr, struct vm_boundaries *area)
 	return ret;
 }
 
-static uint64_t get_pageflags(unsigned long addr)
-{
-	FILE *file;
-	uint64_t pfn;
-	unsigned long offset;
-
-	file = fopen("/proc/self/pagemap", "r");
-	if (!file) {
-		perror("fopen pagemap");
-		_exit(1);
-	}
-
-	offset = addr / getpagesize() * sizeof(pfn);
-
-	if (fseek(file, offset, SEEK_SET)) {
-		perror("fseek pagemap");
-		_exit(1);
-	}
-
-	if (fread(&pfn, sizeof(pfn), 1, file) != 1) {
-		perror("fread pagemap");
-		_exit(1);
-	}
-
-	fclose(file);
-	return pfn;
-}
-
-static uint64_t get_kpageflags(unsigned long pfn)
-{
-	uint64_t flags;
-	FILE *file;
-
-	file = fopen("/proc/kpageflags", "r");
-	if (!file) {
-		perror("fopen kpageflags");
-		_exit(1);
-	}
-
-	if (fseek(file, pfn * sizeof(flags), SEEK_SET)) {
-		perror("fseek kpageflags");
-		_exit(1);
-	}
-
-	if (fread(&flags, sizeof(flags), 1, file) != 1) {
-		perror("fread kpageflags");
-		_exit(1);
-	}
-
-	fclose(file);
-	return flags;
-}
-
 #define VMFLAGS "VmFlags:"
 
 static bool is_vmflag_set(unsigned long addr, const char *vmflag)
@@ -159,19 +106,13 @@ static bool is_vmflag_set(unsigned long addr, const char *vmflag)
 #define RSS  "Rss:"
 #define LOCKED "lo"
 
-static bool is_vma_lock_on_fault(unsigned long addr)
+static unsigned long get_value_for_name(unsigned long addr, const char *name)
 {
-	bool ret = false;
-	bool locked;
-	FILE *smaps = NULL;
-	unsigned long vma_size, vma_rss;
 	char *line = NULL;
-	char *value;
 	size_t size = 0;
-
-	locked = is_vmflag_set(addr, LOCKED);
-	if (!locked)
-		goto out;
+	char *value_ptr;
+	FILE *smaps = NULL;
+	unsigned long value = -1UL;
 
 	smaps = seek_to_smaps_entry(addr);
 	if (!smaps) {
@@ -179,44 +120,43 @@ static bool is_vma_lock_on_fault(unsigned long addr)
 		goto out;
 	}
 
-	while (getline(&line, &size, smaps) > 0) {
-		if (!strstr(line, SIZE)) {
+	while (getline(&line, &size, file) > 0) {
+		if (!strstr(line, name)) {
 			free(line);
 			line = NULL;
 			size = 0;
 			continue;
 		}
 
-		value = line + strlen(SIZE);
-		if (sscanf(value, "%lu kB", &vma_size) < 1) {
+		value_ptr = line + strlen(name);
+		if (sscanf(value_ptr, "%lu kB", &value) < 1) {
 			printf("Unable to parse smaps entry for Size\n");
 			goto out;
 		}
 		break;
 	}
 
-	while (getline(&line, &size, smaps) > 0) {
-		if (!strstr(line, RSS)) {
-			free(line);
-			line = NULL;
-			size = 0;
-			continue;
-		}
-
-		value = line + strlen(RSS);
-		if (sscanf(value, "%lu kB", &vma_rss) < 1) {
-			printf("Unable to parse smaps entry for Rss\n");
-			goto out;
-		}
-		break;
-	}
-
-	ret = locked && (vma_rss < vma_size);
 out:
-	free(line);
 	if (smaps)
 		fclose(smaps);
-	return ret;
+	free(line);
+	return value;
+}
+
+static bool is_vma_lock_on_fault(unsigned long addr)
+{
+	bool locked;
+	unsigned long vma_size, vma_rss;
+
+	locked = is_vmflag_set(addr, LOCKED);
+	if (!locked)
+		return false
+
+	vma_size = get_value_for_name(addr, SIZE);
+	vma_rss = get_value_for_name(addr, RSS);
+
+	/* only one page is faulted in */
+	return (vma_rss < vma_size);
 }
 
 #define PRESENT_BIT     0x8000000000000000ULL
@@ -225,40 +165,18 @@ static bool is_vma_lock_on_fault(unsigned long addr)
 
 static int lock_check(char *map)
 {
-	unsigned long page_size = getpagesize();
-	uint64_t page1_flags, page2_flags;
-
-	page1_flags = get_pageflags((unsigned long)map);
-	page2_flags = get_pageflags((unsigned long)map + page_size);
-
-	/* Both pages should be present */
-	if (((page1_flags & PRESENT_BIT) == 0) ||
-	    ((page2_flags & PRESENT_BIT) == 0)) {
-		printf("Failed to make both pages present\n");
-		return 1;
-	}
-
-	page1_flags = get_kpageflags(page1_flags & PFN_MASK);
-	page2_flags = get_kpageflags(page2_flags & PFN_MASK);
-
-	/* Both pages should be unevictable */
-	if (((page1_flags & UNEVICTABLE_BIT) == 0) ||
-	    ((page2_flags & UNEVICTABLE_BIT) == 0)) {
-		printf("Failed to make both pages unevictable\n");
-		return 1;
-	}
+	bool locked;
+	FILE *smaps = NULL;
+	unsigned long vma_size, vma_rss;
 
-	if (!is_vmflag_set((unsigned long)map, LOCKED)) {
-		printf("VMA flag %s is missing on page 1\n", LOCKED);
-		return 1;
-	}
+	locked = is_vmflag_set(addr, LOCKED);
+	if (!locked)
+		return false;
 
-	if (!is_vmflag_set((unsigned long)map + page_size, LOCKED)) {
-		printf("VMA flag %s is missing on page 2\n", LOCKED);
-		return 1;
-	}
+	vma_size = get_value_for_name(SIZE, smaps);
+	vma_rss = get_value_for_name(RSS, smaps);
 
-	return 0;
+	return (vma_rss == vma_size);
 }
 
 static int unlock_lock_check(char *map)
@@ -266,16 +184,6 @@ static int unlock_lock_check(char *map)
 	unsigned long page_size = getpagesize();
 	uint64_t page1_flags, page2_flags;
 
-	page1_flags = get_pageflags((unsigned long)map);
-	page2_flags = get_pageflags((unsigned long)map + page_size);
-	page1_flags = get_kpageflags(page1_flags & PFN_MASK);
-	page2_flags = get_kpageflags(page2_flags & PFN_MASK);
-
-	if ((page1_flags & UNEVICTABLE_BIT) || (page2_flags & UNEVICTABLE_BIT)) {
-		printf("A page is still marked unevictable after unlock\n");
-		return 1;
-	}
-
 	if (is_vmflag_set((unsigned long)map, LOCKED)) {
 		printf("VMA flag %s is present on page 1 after unlock\n", LOCKED);
 		return 1;
@@ -333,36 +241,7 @@ static int onfault_check(char *map)
 	unsigned long page_size = getpagesize();
 	uint64_t page1_flags, page2_flags;
 
-	page1_flags = get_pageflags((unsigned long)map);
-	page2_flags = get_pageflags((unsigned long)map + page_size);
-
-	/* Neither page should be present */
-	if ((page1_flags & PRESENT_BIT) || (page2_flags & PRESENT_BIT)) {
-		printf("Pages were made present by MLOCK_ONFAULT\n");
-		return 1;
-	}
-
 	*map = 'a';
-	page1_flags = get_pageflags((unsigned long)map);
-	page2_flags = get_pageflags((unsigned long)map + page_size);
-
-	/* Only page 1 should be present */
-	if ((page1_flags & PRESENT_BIT) == 0) {
-		printf("Page 1 is not present after fault\n");
-		return 1;
-	} else if (page2_flags & PRESENT_BIT) {
-		printf("Page 2 was made present\n");
-		return 1;
-	}
-
-	page1_flags = get_kpageflags(page1_flags & PFN_MASK);
-
-	/* Page 1 should be unevictable */
-	if ((page1_flags & UNEVICTABLE_BIT) == 0) {
-		printf("Failed to make faulted page unevictable\n");
-		return 1;
-	}
-
 	if (!is_vma_lock_on_fault((unsigned long)map)) {
 		printf("VMA is not marked for lock on fault\n");
 		return 1;
@@ -381,14 +260,6 @@ static int unlock_onfault_check(char *map)
 	unsigned long page_size = getpagesize();
 	uint64_t page1_flags;
 
-	page1_flags = get_pageflags((unsigned long)map);
-	page1_flags = get_kpageflags(page1_flags & PFN_MASK);
-
-	if (page1_flags & UNEVICTABLE_BIT) {
-		printf("Page 1 is still marked unevictable after unlock\n");
-		return 1;
-	}
-
 	if (is_vma_lock_on_fault((unsigned long)map) ||
 	    is_vma_lock_on_fault((unsigned long)map + page_size)) {
 		printf("VMA is still lock on fault after unlock\n");
@@ -465,17 +336,6 @@ static int test_lock_onfault_of_present()
 		goto unmap;
 	}
 
-	page1_flags = get_pageflags((unsigned long)map);
-	page2_flags = get_pageflags((unsigned long)map + page_size);
-	page1_flags = get_kpageflags(page1_flags & PFN_MASK);
-	page2_flags = get_kpageflags(page2_flags & PFN_MASK);
-
-	/* Page 1 should be unevictable */
-	if ((page1_flags & UNEVICTABLE_BIT) == 0) {
-		printf("Failed to make present page unevictable\n");
-		goto unmap;
-	}
-
 	if (!is_vma_lock_on_fault((unsigned long)map) ||
 	    !is_vma_lock_on_fault((unsigned long)map + page_size)) {
 		printf("VMA with present pages is not marked lock on fault\n");

-- 
Michal Hocko
SUSE Labs