Re: [PATCH 2/2] mm/hmm: Only set FAULT_FLAG_ALLOW_RETRY for non-blocking

[Jerome Glisse <jglisse@redhat.com>]

Andrew can we get this 2 fixes line up for 5.2 ?

On Mon, May 13, 2019 at 07:36:44PM +0000, Kuehling, Felix wrote:
> Hi Jerome,
> 
> Do you want me to push the patches to your branch? Or are you going to 
> apply them yourself?
> 
> Is your hmm-5.2-v3 branch going to make it into Linux 5.2? If so, do you 
> know when? I'd like to coordinate with Dave Airlie so that we can also 
> get that update into a drm-next branch soon.
> 
> I see that Linus merged Dave's pull request for Linux 5.2, which 
> includes the first changes in amdgpu using HMM. They're currently broken 
> without these two patches.

HMM patch do not go through any git branch they go through the mmotm
collection. So it is not something you can easily coordinate with drm
branch.

By broken i expect you mean that if numabalance happens it breaks ?
Or it might sleep when you are not expecting it too ?

Cheers,
Jérôme

> 
> Thanks,
>    Felix
> 
> On 2019-05-10 4:14 p.m., Jerome Glisse wrote:
> > [CAUTION: External Email]
> >
> > On Fri, May 10, 2019 at 07:53:24PM +0000, Kuehling, Felix wrote:
> >> Don't set this flag by default in hmm_vma_do_fault. It is set
> >> conditionally just a few lines below. Setting it unconditionally
> >> can lead to handle_mm_fault doing a non-blocking fault, returning
> >> -EBUSY and unlocking mmap_sem unexpectedly.
> >>
> >> Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
> > Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> >
> >> ---
> >>   mm/hmm.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/mm/hmm.c b/mm/hmm.c
> >> index b65c27d5c119..3c4f1d62202f 100644
> >> --- a/mm/hmm.c
> >> +++ b/mm/hmm.c
> >> @@ -339,7 +339,7 @@ struct hmm_vma_walk {
> >>   static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
> >>                            bool write_fault, uint64_t *pfn)
> >>   {
> >> -     unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_REMOTE;
> >> +     unsigned int flags = FAULT_FLAG_REMOTE;
> >>        struct hmm_vma_walk *hmm_vma_walk = walk->private;
> >>        struct hmm_range *range = hmm_vma_walk->range;
> >>        struct vm_area_struct *vma = walk->vma;
> >> --
> >> 2.17.1
> >>