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 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
>> --- a/include/linux/hmm.h
>> +++ 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.
I can also send a separate patch to then remove hmm_vma_fault()
but I guess that should be after AMD's changes.

> Also, I see in linux-next that amdgpu_ttm.c has wrongly copied use of
> this deprecated API, including these bugs...
> 
> amd folks: Can you please push a patch for your driver to stop using
> hmm_vma_fault() and correct the use-after free? Ideally I'd like to
> delete this function this merge cycle from hmm.git
> 
> Also if you missed it, I'm running a clean hmm.git that you can pull
> into the AMD tree, if necessary, to get the changes that will go into
> 5.3 - if you need/wish to do this please consult with me before making a
> merge commit, thanks. See:
> 
>   https://lore.kernel.org/lkml/20190524124455.GB16845@ziepe.ca/
> 
> So Ralph, you'll need to resend this.
> 
> Thanks,
> Jason
>