Re: [Xen-devel] [PATCH] xen mmu: fix a race window causing leave_mm BUG()

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Apr 29, 2011 at 12:10:57PM +0800, Tian, Kevin wrote:
>     xen mmu: fix a race window causing leave_mm BUG()

I've this in mailbox and I am wondering whether this still an issue with the 
2.6.39 type kernels?
How do you reproduce the failure? When using LVM?
>     
>     there's a race window in xen_drop_mm_ref, where remote cpu may exit
>     dirty bitmap between the check on this cpu and the point where remote
>     cpu handles drop request. So in drop_other_mm_ref we need check
>     whether TLB state is still lazy before calling into leave_mm. This
>     bug is rarely observed in earlier kernel, but exaggerated by the
>     commit 831d52bc153971b70e64eccfbed2b232394f22f8 which clears bitmap
>     after changing the TLB state.
>     
>     thanks for Maxiaoyun<tinnycloud@xxxxxxxxxxx> to verify it.
>     
>     Signed-off-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 4e5a611..74c6e4a 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -1260,7 +1260,7 @@ static void drop_other_mm_ref(void *info)
>  
>       active_mm = percpu_read(cpu_tlbstate.active_mm);
>  
> -     if (active_mm == mm)
> +     if (active_mm == mm && percpu_read(cpu_tlbstate.state) != TLBSTATE_OK)
>               leave_mm(smp_processor_id());
>  
>       /* If this cpu still has a stale cr3 reference, then make sure


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