diff options
authorLinus Torvalds <torvalds@linux-foundation.org>2011-05-04 21:30:28 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-05-04 21:30:28 -0700
commita1fde08c74e90accd62d4cfdbf580d2ede938fe7 (patch)
parent5895198c56d131cc696556a45f7ff0ea99ac297b (diff)
VM: skip the stack guard page lookup in get_user_pages only for mlock
The logic in __get_user_pages() used to skip the stack guard page lookup whenever the caller wasn't interested in seeing what the actual page was. But Michel Lespinasse points out that there are cases where we don't care about the physical page itself (so 'pages' may be NULL), but do want to make sure a page is mapped into the virtual address space. So using the existence of the "pages" array as an indication of whether to look up the guard page or not isn't actually so great, and we really should just use the FOLL_MLOCK bit. But because that bit was only set for the VM_LOCKED case (and not all vma's necessarily have it, even for mlock()), we couldn't do that originally. Fix that by moving the VM_LOCKED check deeper into the call-chain, which actually simplifies many things. Now mlock() gets simpler, and we can also check for FOLL_MLOCK in __get_user_pages() and the code ends up much more straightforward. Reported-and-reviewed-by: Michel Lespinasse <walken@google.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2 files changed, 4 insertions, 8 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 607098d47e74..27f425378112 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1359,7 +1359,7 @@ split_fallthrough:
- if (flags & FOLL_MLOCK) {
+ if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
* The preliminary mapping check is mainly to avoid the
* pointless overhead of lock_page on the ZERO_PAGE
@@ -1552,10 +1552,9 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
- * If we don't actually want the page itself,
- * and it's the stack guard page, just skip it.
+ * For mlock, just skip the stack guard page.
- if (!pages && stack_guard_page(vma, start))
+ if ((gup_flags & FOLL_MLOCK) && stack_guard_page(vma, start))
goto next_page;
do {
diff --git a/mm/mlock.c b/mm/mlock.c
index 6b55e3efe0df..516b2c2ddd5a 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -162,7 +162,7 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
VM_BUG_ON(end > vma->vm_end);
- gup_flags = FOLL_TOUCH;
+ gup_flags = FOLL_TOUCH | FOLL_MLOCK;
* We want to touch writable mappings with a write fault in order
* to break COW, except for shared mappings because these don't COW
@@ -178,9 +178,6 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
gup_flags |= FOLL_FORCE;
- if (vma->vm_flags & VM_LOCKED)
- gup_flags |= FOLL_MLOCK;
return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
NULL, NULL, nonblocking);