mm/mincore: handle non-swap entries before !CONFIG_SWAP guard

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

Posted by Usama Arif 5 days, 11 hours ago

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>
---
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;
 
+	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

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

Posted by Johannes Weiner 4 days, 13 hours ago

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>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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

Posted by Lorenzo Stoakes 4 days, 16 hours ago

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
>

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

Posted by Usama Arif 4 days, 16 hours ago


On 03/06/2026 13:08, Lorenzo Stoakes wrote:
> 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?

Yes, thats right. In softleaf_is_swap(), softleaf_type() returns SOFTLEAF_SWAP
iff type_num < MAX_SWAPFILES. MAX_SWAPFILES is a compile-time constant independent
of CONFIG_SWAP, so softleaf_is_swap() isn't structurally gated, but every producer
of real swap entries lives under CONFIG_SWAP.
With !CONFIG_SWAP none of those run, so softleaf_is_swap() is always 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
>>

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

Posted by Kairui Song 5 days, 1 hour ago

On Wed, Jun 3, 2026 at 1:23 AM Usama Arif <usama.arif@linux.dev> 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>
> ---
> 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;
>
> +       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

Looks good to me, thanks!

Reviewed-by: Kairui Song <kasong@tencent.com>

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

Posted by Pedro Falcato 5 days, 10 hours ago

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>

LGTM, thanks!

Reviewed-by: Pedro Falcato <pfalcato@suse.de>

Maybe Cc: stable@kernel.org ?

-- 
Pedro

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

Posted by Usama Arif 4 days, 18 hours ago


On 02/06/2026 18:51, Pedro Falcato wrote:
> 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>
> 
> LGTM, thanks!
> 
> Reviewed-by: Pedro Falcato <pfalcato@suse.de>
> 
> Maybe Cc: stable@kernel.org ?
> 

Ah yes, I have cc-ed stable in the reply to this email, but probably that
is not enough?

Thanks

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

Posted by Lorenzo Stoakes 4 days, 16 hours ago

On Wed, Jun 03, 2026 at 10:52:24AM +0100, Usama Arif wrote:
>
>
> On 02/06/2026 18:51, Pedro Falcato wrote:
> > 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>
> >
> > LGTM, thanks!
> >
> > Reviewed-by: Pedro Falcato <pfalcato@suse.de>
> >
> > Maybe Cc: stable@kernel.org ?
> >
>
> Ah yes, I have cc-ed stable in the reply to this email, but probably that
> is not enough?

Yeah I think a Cc: in the body is required, but then again Andrew does add Cc's
for Cc'd parties so maybe it'll be automagically sorted out.

Andrew - probably we're good here but just checking to be sure?

>
> Thanks

Thanks, Lorenzo

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

Posted by Andrew Morton 4 days, 10 hours ago

On Wed, 3 Jun 2026 13:07:04 +0100 Lorenzo Stoakes <ljs@kernel.org> wrote:

> > >> Fixes: 1f2052755c15 ("mm/mincore: use a helper for checking the swap cache")
> > >> Signed-off-by: Usama Arif <usama.arif@linux.dev>
> > >
> > > LGTM, thanks!
> > >
> > > Reviewed-by: Pedro Falcato <pfalcato@suse.de>
> > >
> > > Maybe Cc: stable@kernel.org ?
> > >
> >
> > Ah yes, I have cc-ed stable in the reply to this email, but probably that
> > is not enough?
> 
> Yeah I think a Cc: in the body is required,

It's required for MM patches because we've asked the -stable
maintainers to not auto-pick everything which has a Fixes:.

> but then again Andrew does add Cc's
> for Cc'd parties so maybe it'll be automagically sorted out.

cc:stable management is all manual here.

> Andrew - probably we're good here but just checking to be sure?

Yep, I'd added it thanks.  But please always do check!