On Sun, Feb 17, 2013 at 02:35:52AM -0000, Samu Kallio wrote:
> In paravirtualized x86_64 kernels, vmalloc_fault may cause an oops
> when lazy MMU updates are enabled, because set_pgd effects are being
> deferred.
>
> One instance of this problem is during process mm cleanup with memory
> cgroups enabled. The chain of events is as follows:
>
> - zap_pte_range enables lazy MMU updates
> - zap_pte_range eventually calls mem_cgroup_charge_statistics,
> which accesses the vmalloc'd mem_cgroup per-cpu stat area
> - vmalloc_fault is triggered which tries to sync the corresponding
> PGD entry with set_pgd, but the update is deferred
> - vmalloc_fault oopses due to a mismatch in the PUD entries
>
> Calling arch_flush_lazy_mmu_mode immediately after set_pgd makes the
> changes visible to the consistency checks.
How do you reproduce this? Is there a BUG() or WARN() trace that
is triggered when this happens?
Also pls next time also CC me.
>
> Signed-off-by: Samu Kallio <samu.kal...@aberdeencloud.com>
>
> ---
> arch/x86/mm/fault.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 8e13ecb..0a45298 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -378,10 +378,12 @@ static noinline __kprobes int vmalloc_fault(unsigned
> long address)
> if (pgd_none(*pgd_ref))
> return -1;
>
> - if (pgd_none(*pgd))
> + if (pgd_none(*pgd)) {
> set_pgd(pgd, *pgd_ref);
> - else
> + arch_flush_lazy_mmu_mode();
> + } else {
> BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
> + }
>
> /*
> * Below here mismatches are bugs because these lower tables
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
