linux-kernel - Re: [PATCH] mm/memblock: replace u64 with phys_addr

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Message-ID: <20180704132905.GS22503@dhcp22.suse.cz>
Date:   Wed, 4 Jul 2018 15:29:05 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] mm/memblock: replace u64 with phys_addr_t where
 appropriate

On Wed 04-07-18 16:24:11, Mike Rapoport wrote:
> On Wed, Jul 04, 2018 at 03:05:00PM +0200, Michal Hocko wrote:
> > On Tue 03-07-18 20:05:06, Mike Rapoport wrote:
> > > Most functions in memblock already use phys_addr_t to represent a physical
> > > address with __memblock_free_late() being an exception.
> > > 
> > > This patch replaces u64 with phys_addr_t in __memblock_free_late() and
> > > switches several format strings from %llx to %pa to avoid casting from
> > > phys_addr_t to u64.
> > > 
> > > CC: Michal Hocko <mhocko@...nel.org>
> > > CC: Matthew Wilcox <willy@...radead.org>
> > > Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> > > ---
> > >  mm/memblock.c | 46 +++++++++++++++++++++++-----------------------
> > >  1 file changed, 23 insertions(+), 23 deletions(-)
> > > 
> > > diff --git a/mm/memblock.c b/mm/memblock.c
> > > index 03d48d8..20ad8e9 100644
> > > --- a/mm/memblock.c
> > > +++ b/mm/memblock.c
> > > @@ -330,7 +330,7 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
> > >  {
> > >  	struct memblock_region *new_array, *old_array;
> > >  	phys_addr_t old_alloc_size, new_alloc_size;
> > > -	phys_addr_t old_size, new_size, addr;
> > > +	phys_addr_t old_size, new_size, addr, new_end;
> > >  	int use_slab = slab_is_available();
> > >  	int *in_slab;
> > >  
> > > @@ -391,9 +391,9 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
> > >  		return -1;
> > >  	}
> > >  
> > > -	memblock_dbg("memblock: %s is doubled to %ld at [%#010llx-%#010llx]",
> > > -			type->name, type->max * 2, (u64)addr,
> > > -			(u64)addr + new_size - 1);
> > > +	new_end = addr + new_size - 1;
> > > +	memblock_dbg("memblock: %s is doubled to %ld at [%pa-%pa]",
> > > +			type->name, type->max * 2, &addr, &new_end);
> > 
> > I didn't get to check this carefully but this surely looks suspicious. I
> > am pretty sure you wanted to print the value here rather than address of
> > the local variable, right?
> 
> It's the semantics of %pa:
> 
> Physical address types phys_addr_t
> ----------------------------------
> 
> ::
> 
> 	%pa[p]	0x01234567 or 0x0123456789abcdef
> 
> For printing a phys_addr_t type (and its derivatives, such as
> resource_size_t) which can vary based on build options, regardless of the
> width of the CPU data path.
> 
> Passed by reference.

I wasn't aware of that. Thanks for the clarification!

-- 
Michal Hocko
SUSE Labs