From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id 86F916B006A for ; Fri, 23 Jan 2009 12:34:40 -0500 (EST) Date: Fri, 23 Jan 2009 18:34:21 +0100 From: Ingo Molnar Subject: Re: [PATCH] x86,mm: fix pte_free() Message-ID: <20090123173421.GA30980@elte.hu> References: <1232728669.4826.143.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1232728669.4826.143.camel@laptop> Sender: owner-linux-mm@kvack.org To: Peter Zijlstra Cc: Linus Torvalds , Nick Piggin , Hugh Dickins , Thomas Gleixner , Andrew Morton , L-K , linux-mm , David Howells List-ID: * Peter Zijlstra wrote: > On -rt we were seeing spurious bad page states like: > > Bad page state in process 'firefox' > page:c1bc2380 flags:0x40000000 mapping:c1bc2390 mapcount:0 count:0 > Trying to fix it up, but a reboot is needed > Backtrace: > Pid: 503, comm: firefox Not tainted 2.6.26.8-rt13 #3 > [] ? printk+0x14/0x19 > [] bad_page+0x4e/0x79 > [] free_hot_cold_page+0x5b/0x1d3 > [] free_hot_page+0xf/0x11 > [] __free_pages+0x20/0x2b > [] __pte_alloc+0x87/0x91 > [] handle_mm_fault+0xe4/0x733 > [] ? rt_mutex_down_read_trylock+0x57/0x63 > [] ? rt_mutex_down_read_trylock+0x57/0x63 > [] do_page_fault+0x36f/0x88a > > This is the case where a concurrent fault already installed the PTE and > we get to free the newly allocated one. > > This is due to pgtable_page_ctor() doing the spin_lock_init(&page->ptl) > which is overlaid with the {private, mapping} struct. > > union { > struct { > unsigned long private; > struct address_space *mapping; > }; > #if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS > spinlock_t ptl; > #endif > struct kmem_cache *slab; > struct page *first_page; > }; > > Normally the spinlock is small enough to not stomp on page->mapping, but > PREEMPT_RT=y has huge 'spin'locks. > > But lockdep kernels should also be able to trigger this splat, as the > lock tracking code grows the spinlock to cover page->mapping. > > The obvious fix is calling pgtable_page_dtor() like the regular pte free > path __pte_free_tlb() does. > > It seems all architectures except x86 and nm10300 already do this, and > nm10300 doesn't seem to use pgtable_page_ctor(), which suggests it > doesn't do SMP or simply doesnt do MMU at all or something. > > Signed-off-by: Peter Zijlstra > CC: stable@kernel.org > --- > arch/x86/include/asm/pgalloc.h | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h > index cb7c151..b99023c 100644 > --- a/arch/x86/include/asm/pgalloc.h > +++ b/arch/x86/include/asm/pgalloc.h > @@ -42,6 +42,7 @@ static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte) > > static inline void pte_free(struct mm_struct *mm, struct page *pte) > { > + pgtable_page_dtor(); i suspect on lockdep we dont see this in practice because it initializes things to NULL, which hides the issue. On -rt we initialize list heads there which brings up the wrong warning in the page free logic. So i agree with the fix, but the patch does not look right: shouldnt that be pgtable_page_dtor(pte), so that we get ->mapping cleared via pte_lock_deinit()? (which i guess your intention was here - this probably wont even build) Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org