lkml.org 
[lkml]   [2009]   [Jan]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] x86,mm: fix pte_free()

* Peter Zijlstra <peterz@infradead.org> 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
> ---
> 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


\
 
 \ /
  Last update: 2009-01-23 18:37    [W:0.077 / U:0.352 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site