On 6/6/19 11:44 AM, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxx>
> Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> ---
> 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. */
That comment can also be deleted, as it has the same meaning as
the WARN_ON() that you just added.
> - 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. */
To be precise, we are poisoning the range's back pointer to it's
owning hmm instance. Maybe this is clearer:
/*
* The range is now invalid, so poison it's hmm pointer.
* Leave other range-> fields in place, for the caller's use.
*/
...or something like that?
> + range->valid = false;
> + memset(&range->hmm, POISON_INUSE, sizeof(range->hmm));
> }
> EXPORT_SYMBOL(hmm_range_unregister);
>
>
The above are very minor documentation points, so:
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
thanks,
--
John Hubbard
NVIDIA
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