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 intentionally removes page==NULL check after pte_page. This
is justified because pte_page() never returns NULL for any architectures
or configurations.
This patch changes the behavior of follow_huge_pmd() for tail pages and
then tail pages can be pinned/returned. So the caller must be changed to
properly handle the returned tail pages.
We could have a choice to add the similar locking to follow_huge_(addr|pud)
for consistency, but it's not necessary because currently these functions
don't support FOLL_GET flag, so let's leave it for future development.
Here is the reproducer:
$ 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)
Fixes: e632a938d914 ("mm: migrate: add hugepage migration code to move_pages()")
Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # [3.12+]
---
ChangeLog v4:
- remove changes related to taking ptl from follow_huge_(addr|pud)(),
which is not neccessary because these functions don't support FOLL_GET
at least for now
- add justification of removing page==NULL check to patch description
- stop changing parameter mm to vma in follow_huge_(pud|pmd)()
- use pmd_lockptr() instead of huge_pte_lock() in follow_huge_pmd()
- use get_page() instead of get_page_unless_zero() in follow_huge_pmd()
- use Fixes: tag and move changelog under '---'
ChangeLog v3:
- remove unnecessary if (page) check
- check (pmd|pud)_huge again after holding ptl
- do the same change also on follow_huge_pud()
- take page table lock also in follow_huge_addr()
ChangeLog v2:
- introduce follow_huge_pmd_lock() to do locking in arch-independent code.
---
include/linux/hugetlb.h | 8 ++++----
mm/gup.c | 25 ++++---------------------
mm/hugetlb.c | 30 +++++++++++++++++++-----------
mm/migrate.c | 3 ++-
4 files changed, 29 insertions(+), 37 deletions(-)
diff --git mmotm-2014-09-09-14-42.orig/include/linux/hugetlb.h mmotm-2014-09-09-14-42/include/linux/hugetlb.h
index 6e6d338641fe..14020c7796af 100644
--- mmotm-2014-09-09-14-42.orig/include/linux/hugetlb.h
+++ mmotm-2014-09-09-14-42/include/linux/hugetlb.h
@@ -99,9 +99,9 @@ int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep);
struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address,
int write);
struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
- pmd_t *pmd, int write);
+ pmd_t *pmd, int flags);
struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,
- pud_t *pud, int write);
+ pud_t *pud, int flags);
int pmd_huge(pmd_t pmd);
int pud_huge(pud_t pmd);
unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
@@ -133,8 +133,8 @@ static inline void hugetlb_report_meminfo(struct seq_file *m)
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(mm, addr, pmd, flags) NULL
+#define follow_huge_pud(mm, addr, pud, flags) NULL
#define prepare_hugepage_range(file, addr, len) (-EINVAL)
#define pmd_huge(x) 0
#define pud_huge(x) 0
diff --git mmotm-2014-09-09-14-42.orig/mm/gup.c mmotm-2014-09-09-14-42/mm/gup.c
index 91d044b1600d..4575d23a33b9 100644
--- mmotm-2014-09-09-14-42.orig/mm/gup.c
+++ mmotm-2014-09-09-14-42/mm/gup.c
@@ -162,33 +162,16 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
pud = pud_offset(pgd, address);
if (pud_none(*pud))
return no_page_table(vma, flags);
- if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
- if (flags & FOLL_GET)
- return NULL;
- page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
- return page;
- }
+ if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB)
+ return follow_huge_pud(mm, address, pud, flags);
if (unlikely(pud_bad(*pud)))
return no_page_table(vma, flags);
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(mm, address, pmd, flags);
if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
return no_page_table(vma, flags);
if (pmd_trans_huge(*pmd)) {
diff --git mmotm-2014-09-09-14-42.orig/mm/hugetlb.c mmotm-2014-09-09-14-42/mm/hugetlb.c
index 34351251e164..941832ee3d5a 100644
--- mmotm-2014-09-09-14-42.orig/mm/hugetlb.c
+++ mmotm-2014-09-09-14-42/mm/hugetlb.c
@@ -3668,26 +3668,34 @@ follow_huge_addr(struct mm_struct *mm, unsigned long address,
struct page * __weak
follow_huge_pmd(struct mm_struct *mm, unsigned long address,
- pmd_t *pmd, int write)
+ pmd_t *pmd, int flags)
{
- struct page *page;
+ struct page *page = NULL;
+ spinlock_t *ptl;
- page = pte_page(*(pte_t *)pmd);
- if (page)
- page += ((address & ~PMD_MASK) >> PAGE_SHIFT);
+ ptl = pmd_lockptr(mm, pmd);
+ spin_lock(ptl);
+
+ if (!pmd_huge(*pmd))
+ goto out;
+
+ page = pte_page(*(pte_t *)pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
+
+ if (flags & FOLL_GET)
+ get_page(page);
+out:
+ spin_unlock(ptl);
return page;
}
struct page * __weak
follow_huge_pud(struct mm_struct *mm, unsigned long address,
- pud_t *pud, int write)
+ pud_t *pud, int flags)
{
- struct page *page;
+ if (flags & FOLL_GET)
+ return NULL;
- page = pte_page(*(pte_t *)pud);
- if (page)
- page += ((address & ~PUD_MASK) >> PAGE_SHIFT);
- return page;
+ return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
}
#ifdef CONFIG_MEMORY_FAILURE
diff --git mmotm-2014-09-09-14-42.orig/mm/migrate.c mmotm-2014-09-09-14-42/mm/migrate.c
index 09d489c55c21..29f12ca176d7 100644
--- mmotm-2014-09-09-14-42.orig/mm/migrate.c
+++ mmotm-2014-09-09-14-42/mm/migrate.c
@@ -1246,7 +1246,8 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
goto put_and_set;
if (PageHuge(page)) {
- isolate_huge_page(page, &pagelist);
+ if (PageHead(page))
+ isolate_huge_page(page, &pagelist);
goto put_and_set;
}
--
1.9.3
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