We have a race condition between move_pages() and freeing hugepages,
where move_pages() calls follow_page(FOLL_GET) for hugepages internally
and tries to get its refcount without preventing concurrent freeing.
This race crashes the kernel, so this patch fixes it by moving FOLL_GET
code for hugepages into follow_huge_pmd() with taking the page table lock.
This patch passes the following test. And libhugetlbfs test shows no
regression.
$ cat movepages.c
#include <stdio.h>
#include <stdlib.h>
#include <numaif.h>
#define ADDR_INPUT 0x700000000000UL
#define HPS 0x200000
#define PS 0x1000
int main(int argc, char *argv[]) {
int i;
int nr_hp = strtol(argv[1], NULL, 0);
int nr_p = nr_hp * HPS / PS;
int ret;
void **addrs;
int *status;
int *nodes;
pid_t pid;
pid = strtol(argv[2], NULL, 0);
addrs = malloc(sizeof(char *) * nr_p + 1);
status = malloc(sizeof(char *) * nr_p + 1);
nodes = malloc(sizeof(char *) * nr_p + 1);
while (1) {
for (i = 0; i < nr_p; i++) {
addrs[i] = (void *)ADDR_INPUT + i * PS;
nodes[i] = 1;
status[i] = 0;
}
ret = numa_move_pages(pid, nr_p, addrs, nodes, status,
MPOL_MF_MOVE_ALL);
if (ret == -1)
err("move_pages");
for (i = 0; i < nr_p; i++) {
addrs[i] = (void *)ADDR_INPUT + i * PS;
nodes[i] = 0;
status[i] = 0;
}
ret = numa_move_pages(pid, nr_p, addrs, nodes, status,
MPOL_MF_MOVE_ALL);
if (ret == -1)
err("move_pages");
}
return 0;
}
$ cat hugepage.c
#include <stdio.h>
#include <sys/mman.h>
#include <string.h>
#define ADDR_INPUT 0x700000000000UL
#define HPS 0x200000
int main(int argc, char *argv[]) {
int nr_hp = strtol(argv[1], NULL, 0);
char *p;
while (1) {
p = mmap((void *)ADDR_INPUT, nr_hp * HPS, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
if (p != (void *)ADDR_INPUT) {
perror("mmap");
break;
}
memset(p, 0, nr_hp * HPS);
munmap(p, nr_hp * HPS);
}
}
$ sysctl vm.nr_hugepages=40
$ ./hugepage 10 &
$ ./movepages 10 $(pgrep -f hugepage)
Note for stable inclusion:
This patch fixes e632a938d914 ("mm: migrate: add hugepage migration code
to move_pages()"), so is applicable to -stable kernels which includes it.
ChangeLog v2:
- introduce follow_huge_pmd_lock() to do locking in arch-independent code.
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # [3.12+]
---
include/linux/hugetlb.h | 3 +++
mm/gup.c | 17 ++---------------
mm/hugetlb.c | 27 +++++++++++++++++++++++++++
3 files changed, 32 insertions(+), 15 deletions(-)
diff --git mmotm-2014-07-22-15-58.orig/include/linux/hugetlb.h mmotm-2014-07-22-15-58/include/linux/hugetlb.h
index 41272bcf73f8..194834853d6f 100644
--- mmotm-2014-07-22-15-58.orig/include/linux/hugetlb.h
+++ mmotm-2014-07-22-15-58/include/linux/hugetlb.h
@@ -101,6 +101,8 @@ struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
pmd_t *pmd, int write);
struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,
pud_t *pud, int write);
+struct page *follow_huge_pmd_lock(struct vm_area_struct *vma,
+ unsigned long address, pmd_t *pmd, int flags);
int pmd_huge(pmd_t pmd);
int pud_huge(pud_t pmd);
unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
@@ -134,6 +136,7 @@ static inline void hugetlb_show_meminfo(void)
}
#define follow_huge_pmd(mm, addr, pmd, write) NULL
#define follow_huge_pud(mm, addr, pud, write) NULL
+#define follow_huge_pmd_lock(vma, addr, pmd, flags) NULL
#define prepare_hugepage_range(file, addr, len) (-EINVAL)
#define pmd_huge(x) 0
#define pud_huge(x) 0
diff --git mmotm-2014-07-22-15-58.orig/mm/gup.c mmotm-2014-07-22-15-58/mm/gup.c
index 91d044b1600d..e4bd59efe686 100644
--- mmotm-2014-07-22-15-58.orig/mm/gup.c
+++ mmotm-2014-07-22-15-58/mm/gup.c
@@ -174,21 +174,8 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
pmd = pmd_offset(pud, address);
if (pmd_none(*pmd))
return no_page_table(vma, flags);
- if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
- page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
- if (flags & FOLL_GET) {
- /*
- * Refcount on tail pages are not well-defined and
- * shouldn't be taken. The caller should handle a NULL
- * return when trying to follow tail pages.
- */
- if (PageHead(page))
- get_page(page);
- else
- page = NULL;
- }
- return page;
- }
+ if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB)
+ return follow_huge_pmd_lock(vma, address, pmd, flags);
if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
return no_page_table(vma, flags);
if (pmd_trans_huge(*pmd)) {
diff --git mmotm-2014-07-22-15-58.orig/mm/hugetlb.c mmotm-2014-07-22-15-58/mm/hugetlb.c
index 7263c770e9b3..4437896cd6ed 100644
--- mmotm-2014-07-22-15-58.orig/mm/hugetlb.c
+++ mmotm-2014-07-22-15-58/mm/hugetlb.c
@@ -3687,6 +3687,33 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address,
#endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
+struct page *follow_huge_pmd_lock(struct vm_area_struct *vma,
+ unsigned long address, pmd_t *pmd, int flags)
+{
+ struct page *page;
+ spinlock_t *ptl;
+
+ if (flags & FOLL_GET)
+ ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, (pte_t *)pmd);
+
+ page = follow_huge_pmd(vma->vm_mm, address, pmd, flags & FOLL_WRITE);
+
+ if (flags & FOLL_GET) {
+ /*
+ * Refcount on tail pages are not well-defined and
+ * shouldn't be taken. The caller should handle a NULL
+ * return when trying to follow tail pages.
+ */
+ if (PageHead(page))
+ get_page(page);
+ else
+ page = NULL;
+ spin_unlock(ptl);
+ }
+
+ return page;
+}
+
#ifdef CONFIG_MEMORY_FAILURE
/* Should be called in hugetlb_lock */
--
1.9.3
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