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

Submitted by Christoph Hellwig on July 1, 2019, 6:20 a.m.

Details

Message ID 20190701062020.19239-20-hch@lst.de
State New
Headers show
Series "Series without cover letter" ( rev: 1 ) in Nouveau

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Commit Message

Christoph Hellwig July 1, 2019, 6:20 a.m.
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 <hch@lst.de>
---
 mm/hmm.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

Patch hide | download patch | download mbox

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 		/* If range is no longer valid force retry.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 		/* If range is no longer valid force retry.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))

Comments

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 
<Felix.Kuehling@amd.com>

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 <hch@lst.de>

> ---

>   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))
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 <hch@lst.de>

Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>

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))
>