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Date: Tue, 2 Apr 2024 06:33:55 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Sasha Levin <sashal@kernel.org>, stable@vger.kernel.org,
	Rik van Riel <riel@surriel.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org
Subject: Re: FAILED: Patch "bounds: support non-power-of-two CONFIG_NR_CPUS"
 failed to apply to 5.4-stable tree
Message-ID: <ZguYw9Dke_uq5UZU@casper.infradead.org>
References: <20240327122125.2836828-1-sashal@kernel.org>
 <ZgQowqqGf-E7Cpcz@casper.infradead.org>
 <2024032935-antsy-imitation-1453@gregkh>
 <2024032959-ladies-circling-3a5e@gregkh>
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In-Reply-To: <2024032959-ladies-circling-3a5e@gregkh>

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.