Re: [PATCH v3] userfaultfd: reset err to be 0 when move_pages_ptes succeeded

[Mike Rapoport <rppt@kernel.org>]

Hi Foxie,

On Wed, Aug 19, 2026 at 10:08:24AM +0700, Foxie Flakey wrote:
> 
> During move_pages() operation, when move_pages_ptes() returns EAGAIN,
> the error code is not cleared even after we processed it. This leads
> to a successful retry but then the same pages are retried again due to
> the stale error code. This time move fails because pages are already
> moved, loop is terminated and move_pages() reports a failure.
> Clear the error code once we processes EAGAIN.
> 
> Fixes: 50944692052b ("userfaultfd: opportunistic TLB-flush batching for present pages in MOVE")
> Assisted-by: ChatGPT:GPT-5.6-Luna
> Signed-off-by: Bryan Lim <foxieflakey@gmail.com>

With the authorship changes that Andrew requested

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
> Changes in v3:
> - Updated to use proper sign off.
> 
> Changes in v2:
> - Updated on description to be easier to understood
> - Reset err before retrying, instead of fixing right at the move_pages_ptes
>   branch.
> - Added Assisted-by, received an answer few days ago from linux-newbies IRC
>   that even I just used AI/LLM as "fast path" of git bisect. I still need
>   to add it following
>   https://docs.kernel.org/process/coding-assistants.html doc.
> 
> ---
>  mm/userfaultfd.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index c3adedaaf7d5..ec5d511bd179 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -2085,8 +2085,10 @@ static ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
>  		}
> 
>  		if (err) {
> -			if (err == -EAGAIN)
> +			if (err == -EAGAIN) {
> +				err = 0;
>  				continue;
> +			}
>  			break;
>  		}
> 
> -- 
> 2.55.0
> 

-- 
Sincerely yours,
Mike.