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

[Kirill A. Shutemov]

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.shute...@linux.intel.com>
Reported-by: Dmitry Vyukov <dvyu...@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