[PATCH v2 hmm 09/11] mm/hmm: Poison hmm_range during unregister

[Ira Weiny]

On Thu, Jun 06, 2019 at 03:44:36PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg at mellanox.com>
> 
> Trying to misuse a range outside its lifetime is a kernel bug. Use WARN_ON
> and poison bytes to detect this condition.
> 
> Signed-off-by: Jason Gunthorpe <jgg at mellanox.com>
> Reviewed-by: Jérôme Glisse <jglisse at redhat.com>
> ---
> v2
> - Keep range start/end valid after unregistration (Jerome)
> ---
>  mm/hmm.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 6802de7080d172..c2fecb3ecb11e1 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -937,7 +937,7 @@ void hmm_range_unregister(struct hmm_range *range)
>  	struct hmm *hmm = range->hmm;
>  
>  	/* Sanity check this really should not happen. */
> -	if (hmm == NULL || range->end <= range->start)
> +	if (WARN_ON(range->end <= range->start))
>  		return;
>  
>  	mutex_lock(&hmm->lock);
> @@ -948,7 +948,10 @@ void hmm_range_unregister(struct hmm_range *range)
>  	range->valid = false;
>  	mmput(hmm->mm);
>  	hmm_put(hmm);
> -	range->hmm = NULL;
> +
> +	/* The range is now invalid, leave it poisoned. */
> +	range->valid = false;

No need to set valid false again as you just did this 5 lines above.

Reviewed-by: Ira Weiny <ira.weiny at intel.com>

> +	memset(&range->hmm, POISON_INUSE, sizeof(range->hmm));
>  }
>  EXPORT_SYMBOL(hmm_range_unregister);
>  
> -- 
> 2.21.0
>