diff options
| author | Pravin B Shelar <pshelar@nicira.com> | 2012-05-29 15:06:49 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-05-29 16:22:24 -0700 |
| commit | 5bf5f03c271907978489868a4c72aeb42b5127d2 (patch) | |
| tree | 2d6b283fa5ee83b723fd4b4a8f070ae53c60ebe9 /mm/swap.c | |
| parent | dbda591d920b4c7692725b13e3f68ecb251e9080 (diff) | |
| download | lwn-5bf5f03c271907978489868a4c72aeb42b5127d2.tar.gz lwn-5bf5f03c271907978489868a4c72aeb42b5127d2.zip | |
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.c | 37 |
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 |