linux-kernel - Re: mm/percpu.c: use smarter memory allocation for struct pcpu_alloc

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Date:   Tue, 28 Nov 2017 09:19:49 +0100
From:   Jesper Nilsson <jesper.nilsson@...s.com>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     Tejun Heo <tj@...nel.org>, Guenter Roeck <linux@...ck-us.net>,
        Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Mikael Starvik <starvik@...s.com>,
        Jesper Nilsson <jespern@...s.com>, linux-cris-kernel@...s.com
Subject: Re: mm/percpu.c: use smarter memory allocation for struct
 pcpu_alloc_info (crisv32 hang)

On Mon, Nov 27, 2017 at 03:51:04PM -0500, Nicolas Pitre wrote:
> On Mon, 27 Nov 2017, Tejun Heo wrote:
> 
> > Hello,
> > 
> > On Mon, Nov 27, 2017 at 03:31:52PM -0500, Nicolas Pitre wrote:
> > > So IMHO I don't think reverting the commit is the right thing to do. 
> > > That commit is clearly not at fault here.
> > 
> > It's not about the blame.  We just want to avoid breaking boot in a
> > way which is difficult to debug.  Once cris is fixed, we can re-apply
> > the patch.
> 
> In that case I suggest the following instead. No point penalizing 
> everyone for a single architecture's fault. And this will serve as a 
> visible reminder to the cris people that they need to clean up.
> 
> ----- >8
> Subject: percpu: hack to let the CRIS architecture to boot until they clean up
> 
> Commit 438a506180 ("percpu: don't forget to free the temporary struct 
> pcpu_alloc_info") uncovered a problem on the CRIS architecture where
> the bootmem allocator is initialized with virtual addresses. Given it 
> has:
> 
>     #define __va(x) ((void *)((unsigned long)(x) | 0x80000000))
> 
> then things just work out because the end result is the same whether you
> give this a physical or a virtual address.
> 
> Untill you call memblock_free_early(__pa(address)) that is, because
> values from __pa() don't match with the virtual addresses stuffed in the
> bootmem allocator anymore.
> 
> Avoid freeing the temporary pcpu_alloc_info memory on that architecture
> until they fix things up to let the kernel boot like it did before.
> 
> Signed-off-by: Nicolas Pitre <nico@...aro.org>
> 
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 79e3549cab..50e7fdf840 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2719,7 +2719,11 @@ void __init setup_per_cpu_areas(void)
>  
>  	if (pcpu_setup_first_chunk(ai, fc) < 0)
>  		panic("Failed to initialize percpu areas.");
> +#ifdef CONFIG_CRIS
> +#warning "the CRIS architecture has physical and virtual addresses confused"
> +#else
>  	pcpu_free_alloc_info(ai);
> +#endif
>  }
>  
>  #endif	/* CONFIG_SMP */

Works for me, and thanks.

/^JN - Jesper Nilsson
-- 
               Jesper Nilsson -- jesper.nilsson@...s.com