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authorPravin B Shelar <pshelar@nicira.com>2012-05-29 15:06:49 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-29 16:22:24 -0700
commit5bf5f03c271907978489868a4c72aeb42b5127d2 (patch)
tree2d6b283fa5ee83b723fd4b4a8f070ae53c60ebe9 /mm/swap.c
parentdbda591d920b4c7692725b13e3f68ecb251e9080 (diff)
mm: fix slab->page flags corruption
Transparent huge pages can change page->flags (PG_compound_lock) without taking Slab lock. Since THP can not break slab pages we can safely access compound page without taking compound lock. Specifically this patch fixes a race between compound_unlock() and slab functions which perform page-flags updates. This can occur when get_page()/put_page() is called on a page from slab. [akpm@linux-foundation.org: tweak comment text, fix comment layout, fix label indenting] Reported-by: Amey Bhide <abhide@nicira.com> Signed-off-by: Pravin B Shelar <pshelar@nicira.com> Reviewed-by: Christoph Lameter <cl@linux.com> Acked-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Pekka Enberg <penberg@cs.helsinki.fi> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap.c')
-rw-r--r--mm/swap.c37
1 files changed, 35 insertions, 2 deletions
diff --git a/mm/swap.c b/mm/swap.c
index 5c13f1338972..6fdd72ec15b0 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -82,6 +82,25 @@ static void put_compound_page(struct page *page)
if (likely(page != page_head &&
get_page_unless_zero(page_head))) {
unsigned long flags;
+
+ /*
+ * THP can not break up slab pages so avoid taking
+ * compound_lock(). Slab performs non-atomic bit ops
+ * on page->flags for better performance. In particular
+ * slab_unlock() in slub used to be a hot path. It is
+ * still hot on arches that do not support
+ * this_cpu_cmpxchg_double().
+ */
+ if (PageSlab(page_head)) {
+ if (PageTail(page)) {
+ if (put_page_testzero(page_head))
+ VM_BUG_ON(1);
+
+ atomic_dec(&page->_mapcount);
+ goto skip_lock_tail;
+ } else
+ goto skip_lock;
+ }
/*
* page_head wasn't a dangling pointer but it
* may not be a head page anymore by the time
@@ -92,10 +111,10 @@ static void put_compound_page(struct page *page)
if (unlikely(!PageTail(page))) {
/* __split_huge_page_refcount run before us */
compound_unlock_irqrestore(page_head, flags);
- VM_BUG_ON(PageHead(page_head));
+skip_lock:
if (put_page_testzero(page_head))
__put_single_page(page_head);
- out_put_single:
+out_put_single:
if (put_page_testzero(page))
__put_single_page(page);
return;
@@ -115,6 +134,8 @@ static void put_compound_page(struct page *page)
VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
VM_BUG_ON(atomic_read(&page->_count) != 0);
compound_unlock_irqrestore(page_head, flags);
+
+skip_lock_tail:
if (put_page_testzero(page_head)) {
if (PageHead(page_head))
__put_compound_page(page_head);
@@ -162,6 +183,18 @@ bool __get_page_tail(struct page *page)
struct page *page_head = compound_trans_head(page);
if (likely(page != page_head && get_page_unless_zero(page_head))) {
+
+ /* Ref to put_compound_page() comment. */
+ if (PageSlab(page_head)) {
+ if (likely(PageTail(page))) {
+ __get_page_tail_foll(page, false);
+ return true;
+ } else {
+ put_page(page_head);
+ return false;
+ }
+ }
+
/*
* page_head wasn't a dangling pointer but it
* may not be a head page anymore by the time