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Subject: Re: [PATCH 19/22] mm: always return EBUSY for invalid ranges in
 hmm_range_{fault,snapshot}
To:     Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Ben Skeggs <bskeggs@redhat.com>
CC:     Ira Weiny <ira.weiny@intel.com>, <linux-mm@kvack.org>,
        <nouveau@lists.freedesktop.org>, <dri-devel@lists.freedesktop.org>,
        <linux-nvdimm@lists.01.org>, <linux-pci@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <20190701062020.19239-1-hch@lst.de>
 <20190701062020.19239-20-hch@lst.de>
From:   Ralph Campbell <rcampbell@nvidia.com>
Message-ID: <85c88d71-2c25-38ff-a4a3-bfd66fff72b7@nvidia.com>
Date:   Wed, 3 Jul 2019 10:32:39 -0700
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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   		/* If range is no longer valid force retry.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   		/* If range is no longer valid force retry.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))
>