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

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