Re: [PATCH 19/22] mm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot}

[Ralph Campbell]

On 6/30/19 11:20 PM, Christoph Hellwig wrote:

We should not have two different error codes for the same condition.  In
addition this really complicates the code due to the special handling of
EAGAIN that drops the mmap_sem due to the FAULT_FLAG_ALLOW_RETRY logic
in the core vm.

Signed-off-by: Christoph Hellwig 


Reviewed-by: Ralph Campbell 

Probably should update the "Return:" comment above
hmm_range_snapshot() too.


---
  mm/hmm.c | 8 +++-
  1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index c85ed7d4e2ce..d125df698e2b 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -974,7 +974,7 @@ long hmm_range_snapshot(struct hmm_range *range)
do {
/* If range is no longer valid force retry. */
if (!range->valid)
-   return -EAGAIN;
+   return -EBUSY;
  
  		vma = find_vma(hmm->mm, start);

if (vma == NULL || (vma->vm_flags & device_vma))
@@ -1069,10 +1069,8 @@ long hmm_range_fault(struct hmm_range *range, bool block)
  
  	do {

/* If range is no longer valid force retry. */
-   if (!range->valid) {
-   up_read(&hmm->mm->mmap_sem);
-   return -EAGAIN;
-   }
+   if (!range->valid)
+   return -EBUSY;
  
  		vma = find_vma(hmm->mm, start);

if (vma == NULL || (vma->vm_flags & device_vma))


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Re: [PATCH 19/22] mm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot}

[Kuehling, Felix]

On 2019-07-01 2:20 a.m., Christoph Hellwig wrote:
> We should not have two different error codes for the same condition.  In
> addition this really complicates the code due to the special handling of
> EAGAIN that drops the mmap_sem due to the FAULT_FLAG_ALLOW_RETRY logic
> in the core vm.

I think the comment above hmm_range_snapshot needs an update. Also 
Documentation/vm/hmm.rst shows some example code using 
hmm_range_snapshot that retries on -EAGAIN. That would need to be 
updated to use -EBUSY or remove the retry logic altogether.

Other than that, this patch is Reviewed-by: Felix Kuehling 


Philip, this means we should remove our retry logic again in 
amdgpu_ttm_tt_get_user_pages. According to the comment above 
hmm_range_fault, it can only return -EAGAIN if the block parameter is 
false. I think this statement is now actually true. We set block=true, 
so we can't get -EAGAIN. On -EBUSY we can let 
amdgpu_amdkfd_restore_userptr_worker schedule the retry (which it does 
already anyway).

Regards,
   Felix


>
> Signed-off-by: Christoph Hellwig 
> ---
>   mm/hmm.c | 8 +++-
>   1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index c85ed7d4e2ce..d125df698e2b 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -974,7 +974,7 @@ long hmm_range_snapshot(struct hmm_range *range)
>   do {
>   /* If range is no longer valid force retry. */
>   if (!range->valid)
> - return -EAGAIN;
> + return -EBUSY;
>   
>   vma = find_vma(hmm->mm, start);
>   if (vma == NULL || (vma->vm_flags & device_vma))
> @@ -1069,10 +1069,8 @@ long hmm_range_fault(struct hmm_range *range, bool 
> block)
>   
>   do {
>   /* If range is no longer valid force retry. */
> - if (!range->valid) {
> - up_read(&hmm->mm->mmap_sem);
> - return -EAGAIN;
> - }
> + if (!range->valid)
> + return -EBUSY;
>   
>   vma = find_vma(hmm->mm, start);
>   if (vma == NULL || (vma->vm_flags & device_vma))
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[PATCH 19/22] mm: always return EBUSY for invalid ranges in hmm_range_{fault, snapshot}

[Christoph Hellwig]

We should not have two different error codes for the same condition.  In
addition this really complicates the code due to the special handling of
EAGAIN that drops the mmap_sem due to the FAULT_FLAG_ALLOW_RETRY logic
in the core vm.

Signed-off-by: Christoph Hellwig 
---
 mm/hmm.c | 8 +++-
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index c85ed7d4e2ce..d125df698e2b 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -974,7 +974,7 @@ long hmm_range_snapshot(struct hmm_range *range)
do {
/* If range is no longer valid force retry. */
if (!range->valid)
-   return -EAGAIN;
+   return -EBUSY;
 
vma = find_vma(hmm->mm, start);
if (vma == NULL || (vma->vm_flags & device_vma))
@@ -1069,10 +1069,8 @@ long hmm_range_fault(struct hmm_range *range, bool block)
 
do {
/* If range is no longer valid force retry. */
-   if (!range->valid) {
-   up_read(&hmm->mm->mmap_sem);
-   return -EAGAIN;
-   }
+   if (!range->valid)
+   return -EBUSY;
 
vma = find_vma(hmm->mm, start);
if (vma == NULL || (vma->vm_flags & device_vma))
-- 
2.20.1

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