linux-kernel - Re: [PATCH v2 5/6] arch: simplify several early memory allocations

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Date:   Thu, 6 Dec 2018 19:08:26 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "David S. Miller" <davem@...emloft.net>,
        Guan Xuetao <gxt@....edu.cn>,
        Greentime Hu <green.hu@...il.com>,
        Jonas Bonn <jonas@...thpole.se>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Michal Simek <monstr@...str.eu>,
        Mark Salter <msalter@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Rich Felker <dalias@...c.org>,
        Russell King <linux@...linux.org.uk>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        linux-arm-kernel@...ts.infradead.org, linux-c6x-dev@...ux-c6x.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-sh@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        openrisc@...ts.librecores.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v2 5/6] arch: simplify several early memory allocations

On Mon, Dec 03, 2018 at 06:49:21PM +0200, Mike Rapoport wrote:
> On Mon, Dec 03, 2018 at 05:29:08PM +0100, Sam Ravnborg wrote:
> > Hi Mike.
> > 
> > > index c37955d..2a17665 100644
> > > --- a/arch/sparc/kernel/prom_64.c
> > > +++ b/arch/sparc/kernel/prom_64.c
> > > @@ -34,16 +34,13 @@
> > >  
> > >  void * __init prom_early_alloc(unsigned long size)
> > >  {
> > > -	unsigned long paddr = memblock_phys_alloc(size, SMP_CACHE_BYTES);
> > > -	void *ret;
> > > +	void *ret = memblock_alloc(size, SMP_CACHE_BYTES);
> > >  
> > > -	if (!paddr) {
> > > +	if (!ret) {
> > >  		prom_printf("prom_early_alloc(%lu) failed\n", size);
> > >  		prom_halt();
> > >  	}
> > >  
> > > -	ret = __va(paddr);
> > > -	memset(ret, 0, size);
> > >  	prom_early_allocated += size;
> > >  
> > >  	return ret;
> > 
> > memblock_alloc() calls memblock_alloc_try_nid().
> > And if allocation fails then memblock_alloc_try_nid() calls panic().
> > So will we ever hit the prom_halt() code?
> 
> memblock_phys_alloc_try_nid() also calls panic if an allocation fails. So
> in either case we never reach prom_halt() code.

So we have code here we never reach - not nice.
If the idea is to avoid relying on the panic inside memblock_alloc() then
maybe replace it with a variant that do not call panic?
To make it clear what happens.

	Sam