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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2017-03-09 16:17:23 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-03-09 17:01:10 -0800
commit6ebb4a1b848fe75323135f93e72c78f8780fd268 (patch)
tree8472bcc9573e2bee10f4a8cc1788177bc6eefadc
parent8346242a7e32c4c93316684ad8f45473932586b9 (diff)
downloadlinux-6ebb4a1b848fe75323135f93e72c78f8780fd268.tar.bz2
thp: fix another corner case of munlock() vs. THPs
The following test case triggers BUG() in munlock_vma_pages_range(): int main(int argc, char *argv[]) { int fd; system("mount -t tmpfs -o huge=always none /mnt"); fd = open("/mnt/test", O_CREAT | O_RDWR); ftruncate(fd, 4UL << 20); mmap(NULL, 4UL << 20, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED | MAP_LOCKED, fd, 0); mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED, fd, 0); munlockall(); return 0; } The second mmap() create PTE-mapping of the first huge page in file. It makes kernel munlock the page as we never keep PTE-mapped page mlocked. On munlockall() when we handle vma created by the first mmap(), munlock_vma_page() returns page_mask == 0, as the page is not mlocked anymore. On next iteration follow_page_mask() return tail page, but page_mask is HPAGE_NR_PAGES - 1. It makes us skip to the first tail page of the next huge page and step on VM_BUG_ON_PAGE(PageMlocked(page)). The fix is not use the page_mask from follow_page_mask() at all. It has no use for us. Link: http://lkml.kernel.org/r/20170302150252.34120-1-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: <stable@vger.kernel.org> [4.5+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/mlock.c9
1 files changed, 4 insertions, 5 deletions
diff --git a/mm/mlock.c b/mm/mlock.c
index 1050511f8b2b..02f138244bf5 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -442,7 +442,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
while (start < end) {
struct page *page;
- unsigned int page_mask;
+ unsigned int page_mask = 0;
unsigned long page_increm;
struct pagevec pvec;
struct zone *zone;
@@ -456,8 +456,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
* suits munlock very well (and if somehow an abnormal page
* has sneaked into the range, we won't oops here: great).
*/
- page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,
- &page_mask);
+ page = follow_page(vma, start, FOLL_GET | FOLL_DUMP);
if (page && !IS_ERR(page)) {
if (PageTransTail(page)) {
@@ -468,8 +467,8 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
/*
* Any THP page found by follow_page_mask() may
* have gotten split before reaching
- * munlock_vma_page(), so we need to recompute
- * the page_mask here.
+ * munlock_vma_page(), so we need to compute
+ * the page_mask here instead.
*/
page_mask = munlock_vma_page(page);
unlock_page(page);