FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS" failed to apply to 5.4-stable tree

FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS" failed to apply to 5.4-stable tree

[Sasha Levin]

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From f2d5dcb48f7ba9e3ff249d58fc1fa963d374e66a Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Tue, 10 Oct 2023 15:55:49 +0100
Subject: [PATCH] bounds: support non-power-of-two CONFIG_NR_CPUS

ilog2() rounds down, so for example when PowerPC 85xx sets CONFIG_NR_CPUS
to 24, we will only allocate 4 bits to store the number of CPUs instead of
5.  Use bits_per() instead, which rounds up.  Found by code inspection.
The effect of this would probably be a misaccounting when doing NUMA
balancing, so to a user, it would only be a performance penalty.  The
effects may be more wide-spread; it's hard to tell.

Link: https://lkml.kernel.org/r/20231010145549.1244748-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Fixes: 90572890d202 ("mm: numa: Change page last {nid,pid} into {cpu,pid}")
Reviewed-by: Rik van Riel <riel@surriel.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 kernel/bounds.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bounds.c b/kernel/bounds.c
index b529182e8b04f..c5a9fcd2d6228 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -19,7 +19,7 @@ int main(void)
 	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
 	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
 #ifdef CONFIG_SMP
-	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
+	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
 #endif
 	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
 #ifdef CONFIG_LRU_GEN
-- 
2.43.0

Re: FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS" failed to apply to 5.4-stable tree

[Matthew Wilcox]

On Wed, Mar 27, 2024 at 08:21:25AM -0400, Sasha Levin wrote:
> The patch below does not apply to the 5.4-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Looks like you just need a little more fuzz on the patch.

diff --git a/kernel/bounds.c b/kernel/bounds.c
index 9795d75b09b2..a94e3769347e 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -19,7 +19,7 @@ int main(void)
 	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
 	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
 #ifdef CONFIG_SMP
-	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
+	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
 #endif
 	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
 	/* End of constants */

> Thanks,
> Sasha
> 
> ------------------ original commit in Linus's tree ------------------
> 
> >From f2d5dcb48f7ba9e3ff249d58fc1fa963d374e66a Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Date: Tue, 10 Oct 2023 15:55:49 +0100
> Subject: [PATCH] bounds: support non-power-of-two CONFIG_NR_CPUS
> 
> ilog2() rounds down, so for example when PowerPC 85xx sets CONFIG_NR_CPUS
> to 24, we will only allocate 4 bits to store the number of CPUs instead of
> 5.  Use bits_per() instead, which rounds up.  Found by code inspection.
> The effect of this would probably be a misaccounting when doing NUMA
> balancing, so to a user, it would only be a performance penalty.  The
> effects may be more wide-spread; it's hard to tell.
> 
> Link: https://lkml.kernel.org/r/20231010145549.1244748-1-willy@infradead.org
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Fixes: 90572890d202 ("mm: numa: Change page last {nid,pid} into {cpu,pid}")
> Reviewed-by: Rik van Riel <riel@surriel.com>
> Acked-by: Mel Gorman <mgorman@techsingularity.net>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>  kernel/bounds.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bounds.c b/kernel/bounds.c
> index b529182e8b04f..c5a9fcd2d6228 100644
> --- a/kernel/bounds.c
> +++ b/kernel/bounds.c
> @@ -19,7 +19,7 @@ int main(void)
>  	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
>  	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
>  #ifdef CONFIG_SMP
> -	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
> +	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
>  #endif
>  	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
>  #ifdef CONFIG_LRU_GEN
> -- 
> 2.43.0
> 
> 
> 
> 

Re: FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS" failed to apply to 5.4-stable tree

[Greg KH]

On Wed, Mar 27, 2024 at 02:10:10PM +0000, Matthew Wilcox wrote:
> On Wed, Mar 27, 2024 at 08:21:25AM -0400, Sasha Levin wrote:
> > The patch below does not apply to the 5.4-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> 
> Looks like you just need a little more fuzz on the patch.
> 
> diff --git a/kernel/bounds.c b/kernel/bounds.c
> index 9795d75b09b2..a94e3769347e 100644
> --- a/kernel/bounds.c
> +++ b/kernel/bounds.c
> @@ -19,7 +19,7 @@ int main(void)
>  	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
>  	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
>  #ifdef CONFIG_SMP
> -	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
> +	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
>  #endif
>  	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
>  	/* End of constants */

Now fuzzed, thanks.

greg k-h

Re: FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS" failed to apply to 5.4-stable tree

[Greg KH]

On Fri, Mar 29, 2024 at 02:34:43PM +0100, Greg KH wrote:
> On Wed, Mar 27, 2024 at 02:10:10PM +0000, Matthew Wilcox wrote:
> > On Wed, Mar 27, 2024 at 08:21:25AM -0400, Sasha Levin wrote:
> > > The patch below does not apply to the 5.4-stable tree.
> > > If someone wants it applied there, or to any other stable or longterm
> > > tree, then please email the backport, including the original git commit
> > > id to <stable@vger.kernel.org>.
> > 
> > Looks like you just need a little more fuzz on the patch.
> > 
> > diff --git a/kernel/bounds.c b/kernel/bounds.c
> > index 9795d75b09b2..a94e3769347e 100644
> > --- a/kernel/bounds.c
> > +++ b/kernel/bounds.c
> > @@ -19,7 +19,7 @@ int main(void)
> >  	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
> >  	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
> >  #ifdef CONFIG_SMP
> > -	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
> > +	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
> >  #endif
> >  	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
> >  	/* End of constants */
> 
> Now fuzzed, thanks.

But it breaks the build on 4.19.y, so I'll go drop it from there.  If
you want it added there, please provide a working fix.

thanks,

greg k-h

Re: FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS" failed to apply to 5.4-stable tree

[Matthew Wilcox]

On Fri, Mar 29, 2024 at 06:05:20PM +0100, Greg KH wrote:
> On Fri, Mar 29, 2024 at 02:34:43PM +0100, Greg KH wrote:
> > On Wed, Mar 27, 2024 at 02:10:10PM +0000, Matthew Wilcox wrote:
> > > On Wed, Mar 27, 2024 at 08:21:25AM -0400, Sasha Levin wrote:
> > > > The patch below does not apply to the 5.4-stable tree.
> > > > If someone wants it applied there, or to any other stable or longterm
> > > > tree, then please email the backport, including the original git commit
> > > > id to <stable@vger.kernel.org>.
> > > 
> > > Looks like you just need a little more fuzz on the patch.
> > > 
> > > diff --git a/kernel/bounds.c b/kernel/bounds.c
> > > index 9795d75b09b2..a94e3769347e 100644
> > > --- a/kernel/bounds.c
> > > +++ b/kernel/bounds.c
> > > @@ -19,7 +19,7 @@ int main(void)
> > >  	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
> > >  	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
> > >  #ifdef CONFIG_SMP
> > > -	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
> > > +	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
> > >  #endif
> > >  	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
> > >  	/* End of constants */
> > 
> > Now fuzzed, thanks.
> 
> But it breaks the build on 4.19.y, so I'll go drop it from there.  If
> you want it added there, please provide a working fix.

Looks like bits_per() didn't exist in 4.19.  It was added as part of commit 69842cba9ace84849bb9b8edcdf2cefccd97901c
Author: Patrick Bellasi <patrick.bellasi@arm.com>
Date:   Fri Jun 21 09:42:02 2019 +0100

    sched/uclamp: Add CPU's clamp buckets refcounting

Up to you; I can provide bits_per() to 4.19 which will aid backporting
other fixes (we currently have 17 uses of bits_per() in 6.9), or we can
just drop this whole thing for 4.19.

Re: FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS" failed to apply to 5.4-stable tree

[Greg KH]

On Tue, Apr 02, 2024 at 06:33:55AM +0100, Matthew Wilcox wrote:
> On Fri, Mar 29, 2024 at 06:05:20PM +0100, Greg KH wrote:
> > On Fri, Mar 29, 2024 at 02:34:43PM +0100, Greg KH wrote:
> > > On Wed, Mar 27, 2024 at 02:10:10PM +0000, Matthew Wilcox wrote:
> > > > On Wed, Mar 27, 2024 at 08:21:25AM -0400, Sasha Levin wrote:
> > > > > The patch below does not apply to the 5.4-stable tree.
> > > > > If someone wants it applied there, or to any other stable or longterm
> > > > > tree, then please email the backport, including the original git commit
> > > > > id to <stable@vger.kernel.org>.
> > > > 
> > > > Looks like you just need a little more fuzz on the patch.
> > > > 
> > > > diff --git a/kernel/bounds.c b/kernel/bounds.c
> > > > index 9795d75b09b2..a94e3769347e 100644
> > > > --- a/kernel/bounds.c
> > > > +++ b/kernel/bounds.c
> > > > @@ -19,7 +19,7 @@ int main(void)
> > > >  	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
> > > >  	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
> > > >  #ifdef CONFIG_SMP
> > > > -	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
> > > > +	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
> > > >  #endif
> > > >  	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
> > > >  	/* End of constants */
> > > 
> > > Now fuzzed, thanks.
> > 
> > But it breaks the build on 4.19.y, so I'll go drop it from there.  If
> > you want it added there, please provide a working fix.
> 
> Looks like bits_per() didn't exist in 4.19.  It was added as part of commit 69842cba9ace84849bb9b8edcdf2cefccd97901c
> Author: Patrick Bellasi <patrick.bellasi@arm.com>
> Date:   Fri Jun 21 09:42:02 2019 +0100
> 
>     sched/uclamp: Add CPU's clamp buckets refcounting
> 
> Up to you; I can provide bits_per() to 4.19 which will aid backporting
> other fixes (we currently have 17 uses of bits_per() in 6.9), or we can
> just drop this whole thing for 4.19.
> 

At this point in time for 4.19, unless it's really criticial, I would
just say drop it.

thanks,

greg k-h