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

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Date:   Mon, 3 Dec 2018 18:49:21 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Sam Ravnborg <sam@...nborg.org>
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 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.

Actually, sparc is rather an exception from the general practice to rely on
panic() inside the early allocator rather than to check the return value.
 
> Do we have a panic() implementation that actually returns?
> 
> 
> > diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
> > index 3c8aac2..52884f4 100644
> > --- a/arch/sparc/mm/init_64.c
> > +++ b/arch/sparc/mm/init_64.c
> > @@ -1089,16 +1089,13 @@ static void __init allocate_node_data(int nid)
> >  	struct pglist_data *p;
> >  	unsigned long start_pfn, end_pfn;
> >  #ifdef CONFIG_NEED_MULTIPLE_NODES
> > -	unsigned long paddr;
> >  
> > -	paddr = memblock_phys_alloc_try_nid(sizeof(struct pglist_data),
> > -					    SMP_CACHE_BYTES, nid);
> > -	if (!paddr) {
> > +	NODE_DATA(nid) = memblock_alloc_node(sizeof(struct pglist_data),
> > +					     SMP_CACHE_BYTES, nid);
> > +	if (!NODE_DATA(nid)) {
> >  		prom_printf("Cannot allocate pglist_data for nid[%d]\n", nid);
> >  		prom_halt();
> >  	}
> > -	NODE_DATA(nid) = __va(paddr);
> > -	memset(NODE_DATA(nid), 0, sizeof(struct pglist_data));
> >  
> >  	NODE_DATA(nid)->node_id = nid;
> >  #endif
> 
> Same here.
> 
> I did not look at the other cases.

I really tried to be careful and did the replacements only for the calls
that do panic if an allocation fails.
 
> 	Sam
> 

-- 
Sincerely yours,
Mike.