Re: [PATCH 4/5] vm/vm_fault.c: check if active_threads is NULL

[Samuel Thibault]

Marin Ramesa, le Tue 19 Nov 2013 07:34:22 +0100, a écrit :
> Check is active_threads is NULL before calling current_task() to
> avoid dereference of null pointer.

Ah, the vm_stat_sample tracing macro is extra careful about
current_thread(), probably because it may be called very early during
boot, but current_thread() really is always non-NULL when vm_fault_page
is called.

> * vm/vm_fault.c (active_threads): Check if it's NULL.
> 
> ---
>  vm/vm_fault.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/vm/vm_fault.c b/vm/vm_fault.c
> index 4b30f98..1089491 100644
> --- a/vm/vm_fault.c
> +++ b/vm/vm_fault.c
> @@ -249,7 +249,8 @@ vm_fault_return_t vm_fault_page(first_object, 
> first_offset,
>  
>       vm_stat_sample(SAMPLED_PC_VM_FAULTS_ANY);
>       vm_stat.faults++;               /* needs lock XXX */
> -     current_task()->faults++;
> +     if (active_threads[(0)] != NULL)        
> +             current_task()->faults++;
>  
>  /*
>   *   Recovery actions
> -- 
> 1.8.1.4
> 
> 

-- 
Samuel
"...Deep Hack Mode--that mysterious and frightening state of
consciousness where Mortal Users fear to tread."
(By Matt Welsh)