Re: [PATCH 5/6] drivers,sgi-gru/grufault.c: call find_vma with the mmap_sem held

[Dimitri Sivanich <sivanich@sgi.com>]

On Sat, Apr 19, 2014 at 07:26:30PM -0700, Davidlohr Bueso wrote:
> From: Jonathan Gonzalez V <zeus@gnu.org>
> 
> Performing vma lookups without taking the mm->mmap_sem is asking
> for trouble. While doing the search, the vma in question can
> be modified or even removed before returning to the caller.
> Take the lock in order to avoid races while iterating through
> the vmacache and/or rbtree.
> 
> This patch is completely *untested*.

The mmap_sem is already taken in all paths calling gru_vtop().

The gru_intr() function takes it before calling gru_try_dropin(), from which
all calls to gru_vtop() originate.

The gru_find_lock_gts() function takes it when called from
gru_handle_user_call_os(), which then calls gru_user_dropin()->gru_try_dropin().

Nacked-by: Dimitri Sivanich <sivanich@sgi.com>

> 
> Signed-off-by: Jonathan Gonzalez V <zeus@gnu.org>
> Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
> Cc: Dimitri Sivanich <sivanich@sgi.com
> ---
>  drivers/misc/sgi-gru/grufault.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> index f74fc0c..15adc84 100644
> --- a/drivers/misc/sgi-gru/grufault.c
> +++ b/drivers/misc/sgi-gru/grufault.c
> @@ -266,6 +266,7 @@ static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
>  	unsigned long paddr;
>  	int ret, ps;
>  
> +	down_write(&mm->mmap_sem);
>  	vma = find_vma(mm, vaddr);
>  	if (!vma)
>  		goto inval;
> @@ -277,22 +278,26 @@ static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
>  	rmb();	/* Must/check ms_range_active before loading PTEs */
>  	ret = atomic_pte_lookup(vma, vaddr, write, &paddr, &ps);
>  	if (ret) {
> -		if (atomic)
> -			goto upm;
> +		if (atomic) {
> +			up_write(&mm->mmap_sem);
> +			return VTOP_RETRY;
> +		}
>  		if (non_atomic_pte_lookup(vma, vaddr, write, &paddr, &ps))
>  			goto inval;
>  	}
>  	if (is_gru_paddr(paddr))
>  		goto inval;
> +
> +	up_write(&mm->mmap_sem);
> +
>  	paddr = paddr & ~((1UL << ps) - 1);
>  	*gpa = uv_soc_phys_ram_to_gpa(paddr);
>  	*pageshift = ps;
>  	return VTOP_SUCCESS;
>  
>  inval:
> +	up_write(&mm->mmap_sem);
>  	return VTOP_INVALID;
> -upm:
> -	return VTOP_RETRY;
>  }
>  
>  
> -- 
> 1.8.1.4

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