Messages in this thread | | | Date | Fri, 23 Jan 2009 18:42:37 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: [PATCH] x86,mm: fix pte_free() |
| |
On Fri, 23 Jan 2009, Peter Zijlstra wrote: > On Fri, 2009-01-23 at 17:37 +0100, 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 > > [<c043d0f3>] ? printk+0x14/0x19 > > [<c0272d4e>] bad_page+0x4e/0x79 > > [<c0273831>] free_hot_cold_page+0x5b/0x1d3 > > [<c02739f6>] free_hot_page+0xf/0x11 > > [<c0273a18>] __free_pages+0x20/0x2b > > [<c027d170>] __pte_alloc+0x87/0x91 > > [<c027d25e>] handle_mm_fault+0xe4/0x733 > > [<c043f680>] ? rt_mutex_down_read_trylock+0x57/0x63 > > [<c043f680>] ? rt_mutex_down_read_trylock+0x57/0x63 > > [<c0218875>] 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 <a.p.zijlsta@chello.nl> > > CC: stable@kernel.org
Thanks, Peter: good catch. That pgtable_page_dtor() had long been there in pte_free(), then somehow got lost in one of 2.6.26's rearrangements.
Acked-by: Hugh Dickins <hugh@veritas.com>
> > Now one that's not obviously borken,..
And I can quite see why you voided the first version: your mind rightly stalled on that foul "struct page *pte". Oh well, clean that up some other time.
Hugh
> > --- > 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..dd14c54 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(pte); > __free_page(pte); > }
| |