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 <[email protected]>
CC: [email protected]
---
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();
__free_page(pte);
}
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 <[email protected]>
> CC: [email protected]
Now one that's not obviously borken,..
---
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);
}
* Peter Zijlstra <[email protected]> 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 <[email protected]>
> CC: [email protected]
> ---
> 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
On Fri, 2009-01-23 at 18:34 +0100, Ingo Molnar wrote:
> 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)
Yeah, I somehow fudged it, already send out a better one. -- One of them
days I guess :-(
* Peter Zijlstra <[email protected]> wrote:
> On Fri, 2009-01-23 at 18:34 +0100, Ingo Molnar wrote:
>
> > 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)
>
> Yeah, I somehow fudged it, already send out a better one. -- One of them
> days I guess :-(
no problem - applied to tip/x86/urgent, thanks Peter!
Ingo
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 <[email protected]>
> > CC: [email protected]
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 <[email protected]>
>
> 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);
> }
Peter Zijlstra <[email protected]> wrote:
> 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.
MN10300 does not, as yet, do SMP.
David
>
> * Peter Zijlstra <[email protected]> wrote:
>
> > On Fri, 2009-01-23 at 18:34 +0100, Ingo Molnar wrote:
> >
> > > 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)
> >
> > Yeah, I somehow fudged it, already send out a better one. -- One of them
> > days I guess :-(
>
> no problem - applied to tip/x86/urgent, thanks Peter!
please fix typo. s/nm10300/MN10300/ :)
at first look, I don't understand his intention.