The patch titled Subject: mm: fix slab->page flags corruption has been added to the -mm tree. Its filename is mm-fix-slab-page-flags-corruption.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Pravin B Shelar <pshelar@xxxxxxxxxx> Subject: 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. Reported-by: Amey Bhide <abhide@xxxxxxxxxx> Signed-off-by: Pravin B Shelar <pshelar@xxxxxxxxxx> Reviewed-by: Christoph Lameter <cl@xxxxxxxxx> Acked-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mm.h | 2 ++ mm/swap.c | 34 +++++++++++++++++++++++++++++++++- 2 files changed, 35 insertions(+), 1 deletion(-) diff -puN include/linux/mm.h~mm-fix-slab-page-flags-corruption include/linux/mm.h --- a/include/linux/mm.h~mm-fix-slab-page-flags-corruption +++ a/include/linux/mm.h @@ -321,6 +321,7 @@ static inline int is_vmalloc_or_module_a static inline void compound_lock(struct page *page) { #ifdef CONFIG_TRANSPARENT_HUGEPAGE + VM_BUG_ON(PageSlab(page)); bit_spin_lock(PG_compound_lock, &page->flags); #endif } @@ -328,6 +329,7 @@ static inline void compound_lock(struct static inline void compound_unlock(struct page *page) { #ifdef CONFIG_TRANSPARENT_HUGEPAGE + VM_BUG_ON(PageSlab(page)); bit_spin_unlock(PG_compound_lock, &page->flags); #endif } diff -puN mm/swap.c~mm-fix-slab-page-flags-corruption mm/swap.c --- a/mm/swap.c~mm-fix-slab-page-flags-corruption +++ a/mm/swap.c @@ -82,6 +82,24 @@ static void put_compound_page(struct pag if (likely(page != page_head && get_page_unless_zero(page_head))) { unsigned long flags; + + /* THP can not break up slab pages, avoid taking + * compound_lock(). Slab prefer non atomic bit ops + * on page->flags for better performance. In particular + * slab_unlock() in slub used to be a hot path + * item. 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 @@ -92,7 +110,7 @@ static void put_compound_page(struct pag 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: @@ -115,6 +133,8 @@ static void put_compound_page(struct pag 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 +182,18 @@ 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 _ Subject: Subject: mm: fix slab->page flags corruption Patches currently in -mm which might be from pshelar@xxxxxxxxxx are mm-fix-slab-page-flags-corruption.patch mm-fix-slab-page-flags-corruption-fix.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html