Re: [PATCH] mm/mincore: handle non-swap entries before !CONFIG_SWAP guard

[Lorenzo Stoakes <ljs@kernel.org>]

On Tue, Jun 02, 2026 at 10:22:47AM -0700, Usama Arif wrote:
> mincore_swap() also fields migration/hwpoison entries (and shmem
> swapin-error entries), which can exist on !CONFIG_SWAP builds when
> CONFIG_MIGRATION or CONFIG_MEMORY_FAILURE is enabled.  The
> !IS_ENABLED(CONFIG_SWAP) guard ran before the non-swap-entry early
> return, so mincore_pte_range() can spuriously WARN and report these
> pages nonresident on !CONFIG_SWAP kernels.
>
> Move the guard below the non-swap-entry check so only true swap
> entries trip the WARN, and migration/hwpoison entries take the
> existing "uptodate / non-shmem" path.
>
> Fixes: 1f2052755c15 ("mm/mincore: use a helper for checking the swap cache")
> Signed-off-by: Usama Arif <usama.arif@linux.dev>

Logic LGTM so:

Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

Small note below but I think not a problem.

Thanks, Lorenzo

> ---
> This was discovered when working on PMD swap entry series
> (https://lore.kernel.org/all/20260602142537.198755-1-usama.arif@linux.dev/)
> ---
>  mm/mincore.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/mm/mincore.c b/mm/mincore.c
> index e5d13eea9234..296f2e3922b5 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -64,11 +64,6 @@ static unsigned char mincore_swap(swp_entry_t entry, bool shmem)
>  	struct folio *folio = NULL;
>  	unsigned char present = 0;
>
> -	if (!IS_ENABLED(CONFIG_SWAP)) {
> -		WARN_ON(1);
> -		return 0;
> -	}
> -
>  	/*
>  	 * Shmem mapping may contain swapin error entries, which are
>  	 * absent. Page table may contain migration or hwpoison
> @@ -77,6 +72,11 @@ static unsigned char mincore_swap(swp_entry_t entry, bool shmem)
>  	if (!softleaf_is_swap(entry))
>  		return !shmem;
>

I guess fine to do this after software_is_swap() because for !CONFIG_SWAP this
will always evaluate false?

Not a big deal therefore I think.

> +	if (!IS_ENABLED(CONFIG_SWAP)) {
> +		WARN_ON(1);
> +		return 0;
> +	}
> +
>  	/*
>  	 * Shmem mapping lookup is lockless, so we need to grab the swap
>  	 * device. mincore page table walk locks the PTL, and the swap
> --
> 2.52.0
>