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SubjectRe: [PATCH 1/6] mm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot}
On Mon, Jul 22, 2019 at 3:14 PM Christoph Hellwig <hch@lst.de> 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>
> Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
> ---
> Documentation/vm/hmm.rst | 2 +-
> mm/hmm.c | 10 ++++------
> 2 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
> index 7d90964abbb0..710ce1c701bf 100644
> --- a/Documentation/vm/hmm.rst
> +++ b/Documentation/vm/hmm.rst
> @@ -237,7 +237,7 @@ The usage pattern is::
> ret = hmm_range_snapshot(&range);
> if (ret) {
> up_read(&mm->mmap_sem);
> - if (ret == -EAGAIN) {
> + if (ret == -EBUSY) {
> /*
> * No need to check hmm_range_wait_until_valid() return value
> * on retry we will get proper error with hmm_range_snapshot()
> diff --git a/mm/hmm.c b/mm/hmm.c
> index e1eedef129cf..16b6731a34db 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -946,7 +946,7 @@ EXPORT_SYMBOL(hmm_range_unregister);
> * @range: range
> * Return: -EINVAL if invalid argument, -ENOMEM out of memory, -EPERM invalid
> * permission (for instance asking for write and range is read only),
> - * -EAGAIN if you need to retry, -EFAULT invalid (ie either no valid
> + * -EBUSY if you need to retry, -EFAULT invalid (ie either no valid
> * vma or it is illegal to access that range), number of valid pages
> * in range->pfns[] (from range start address).
> *
> @@ -967,7 +967,7 @@ 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 /* If range is no longer valid force retry.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))
> @@ -1062,10 +1062,8 @@ 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 /* If range is no longer valid force retry.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;

Is it fine to remove up_read(&hmm->mm->mmap_sem) ?

>
> vma = find_vma(hmm->mm, start);
> if (vma == NULL || (vma->vm_flags & device_vma))
> --
> 2.20.1
>

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