Re: [PATCH 4/5] mm/hmm: hmm_vma_fault() doesn't always call hmm_range_unregister()

[Ralph Campbell <rcampbell@nvidia.com>]

On 6/6/19 12:54 PM, Jason Gunthorpe wrote:
> On Thu, Jun 06, 2019 at 12:44:36PM -0700, Ralph Campbell wrote:
>>
>> On 6/6/19 7:50 AM, Jason Gunthorpe wrote:
>>> On Mon, May 06, 2019 at 04:29:41PM -0700, rcampbell@nvidia.com wrote:
>>>> From: Ralph Campbell <rcampbell@nvidia.com>
>>>>
>>>> The helper function hmm_vma_fault() calls hmm_range_register() but is
>>>> missing a call to hmm_range_unregister() in one of the error paths.
>>>> This leads to a reference count leak and ultimately a memory leak on
>>>> struct hmm.
>>>>
>>>> Always call hmm_range_unregister() if hmm_range_register() succeeded.
>>>>
>>>> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
>>>> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
>>>> Cc: John Hubbard <jhubbard@nvidia.com>
>>>> Cc: Ira Weiny <ira.weiny@intel.com>
>>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>>> Cc: Balbir Singh <bsingharora@gmail.com>
>>>> Cc: Dan Carpenter <dan.carpenter@oracle.com>
>>>> Cc: Matthew Wilcox <willy@infradead.org>
>>>> Cc: Souptick Joarder <jrdr.linux@gmail.com>
>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>>    include/linux/hmm.h | 3 ++-
>>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>>> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
>>>> index 35a429621e1e..fa0671d67269 100644
>>>> +++ b/include/linux/hmm.h
>>>> @@ -559,6 +559,7 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
>>>>    		return (int)ret;
>>>>    	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
>>>> +		hmm_range_unregister(range);
>>>>    		/*
>>>>    		 * The mmap_sem was taken by driver we release it here and
>>>>    		 * returns -EAGAIN which correspond to mmap_sem have been
>>>> @@ -570,13 +571,13 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
>>>>    	ret = hmm_range_fault(range, block);
>>>>    	if (ret <= 0) {
>>>> +		hmm_range_unregister(range);
>>>
>>> While this seems to be a clear improvement, it seems there is still a
>>> bug in nouveau_svm.c around here as I see it calls hmm_vma_fault() but
>>> never calls hmm_range_unregister() for its on stack range - and
>>> hmm_vma_fault() still returns with the range registered.
>>>
>>> As hmm_vma_fault() is only used by nouveau and is marked as
>>> deprecated, I think we need to fix nouveau, either by dropping
>>> hmm_range_fault(), or by adding the missing unregister to nouveau in
>>> this patch.
>>
>> I will send a patch for nouveau to use hmm_range_register() and
>> hmm_range_fault() and do some testing with OpenCL.
> 
> wow, thanks, I'd like to also really like to send such a thing through
> hmm.git - do you know who the nouveau maintainers are so we can
> collaborate on patch planning this?

Ben Skeggs <bskeggs@redhat.com> is the maintainer and
nouveau@lists.freedesktop.org is the mailing list for changes.
I'll be sure to CC them for the patch.

>> I can also send a separate patch to then remove hmm_vma_fault()
>> but I guess that should be after AMD's changes.
> 
> Let us wait to hear back from AMD how they can consume hmm.git - I'd
> very much like to get everything done in one kernel cycle!
> 
> Regards,
> Jason
>