Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1324251 > unrolled thread

[PATCHv2 0/2] Fix another VM_BUG_ON_PAGE(PageTail(page)) on mbind(2)

Back to article view | Back to linux.kernel

Contents

  [PATCHv2 0/2] Fix another VM_BUG_ON_PAGE(PageTail(page)) on mbind(2) "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-02-02 17:30 +0100
    [PATCHv2 1/2] mempolicy: do not try to queue pages from !vma_migratable() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-02-02 17:30 +0100

#1324251 — [PATCHv2 0/2] Fix another VM_BUG_ON_PAGE(PageTail(page)) on mbind(2)

Dmitry Vyukov reported yet another VM_BUG_ON_PAGE(PageTail(page)) bug from
isolate_lru_page().

The fisrt patch fixes the bug by filter out non migratable VMAs in
queue_pages_test_walk(). There's no point to queue pages from non-migratable
VMA even for MPOL_MF_STRICT.

The second patch replace VM_BUG_ON_PAGE() with WARN_RATELIMIT() in
isolate_lru_page(). Most attempts to isolate tail pages are not fatal, as
these pages usually are not on LRU and will not be isolated.

v2:
 - address feedback from Michal Hocko;

Kirill A. Shutemov (2):
  mempolicy: do not try to queue pages from !vma_migratable()
  mm: downgrade VM_BUG in isolate_lru_page() to warning

 mm/mempolicy.c | 14 +++++---------
 mm/vmscan.c    |  2 +-
 2 files changed, 6 insertions(+), 10 deletions(-)

-- 
2.7.0

[toc] | [next] | [standalone]

#1324255 — [PATCHv2 1/2] mempolicy: do not try to queue pages from !vma_migratable()

Maybe I miss some point, but I don't see a reason why we try to queue
pages from non migratable VMAs.

This testcase steps on VM_BUG_ON_PAGE() in isolate_lru_page():

	#include <fcntl.h>
	#include <unistd.h>
	#include <stdio.h>
	#include <sys/mman.h>
	#include <numaif.h>

	#define SIZE 0x2000

	int foo;

	int main()
	{
		int fd;
		char *p;
		unsigned long mask = 2;

		fd = open("/dev/sg0", O_RDWR);
		p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
		/* Faultin pages */
		foo = p[0] + p[0x1000];
		mbind(p, SIZE, MPOL_BIND, &mask, 4, MPOL_MF_MOVE | MPOL_MF_STRICT);
		return 0;
	}

The only case when we can queue pages from such VMA is MPOL_MF_STRICT
plus MPOL_MF_MOVE or MPOL_MF_MOVE_ALL for VMA which has pages on LRU,
but gfp mask is not sutable for migaration (see mapping_gfp_mask() check
in vma_migratable()). That's looks like a bug to me.

Let's filter out non-migratable vma at start of queue_pages_test_walk()
and go to queue_pages_pte_range() only if MPOL_MF_MOVE or
MPOL_MF_MOVE_ALL flag is set.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
---
 mm/mempolicy.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 27d135408a22..4c4187c0e1de 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -548,8 +548,7 @@ retry:
 			goto retry;
 		}
 
-		if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
-			migrate_page_add(page, qp->pagelist, flags);
+		migrate_page_add(page, qp->pagelist, flags);
 	}
 	pte_unmap_unlock(pte - 1, ptl);
 	cond_resched();
@@ -625,7 +624,7 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
 	unsigned long endvma = vma->vm_end;
 	unsigned long flags = qp->flags;
 
-	if (vma->vm_flags & VM_PFNMAP)
+	if (!vma_migratable(vma))
 		return 1;
 
 	if (endvma > end)
@@ -644,16 +643,13 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
 
 	if (flags & MPOL_MF_LAZY) {
 		/* Similar to task_numa_work, skip inaccessible VMAs */
-		if (vma_migratable(vma) &&
-			vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))
+		if (vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))
 			change_prot_numa(vma, start, endvma);
 		return 1;
 	}
 
-	if ((flags & MPOL_MF_STRICT) ||
-	    ((flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) &&
-	     vma_migratable(vma)))
-		/* queue pages from current vma */
+	/* queue pages from current vma */
+	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
 		return 0;
 	return 1;
 }
-- 
2.7.0

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web