Re: [PATCH AUTOSEL 5.3 169/203] x86/platform/uv: Fix kmalloc() NULL check routine

[Mike Travis]

On 10/2/2019 1:34 AM, David Laight wrote:
> From: Sasha Levin
> > Sent: 01 October 2019 17:06
> > Subject: Re: [PATCH AUTOSEL 5.3 169/203] x86/platform/uv: Fix kmalloc() NULL check routine
> >
> > On Sun, Sep 22, 2019 at 10:25:44PM +0200, Greg KH wrote:
> > > On Sun, Sep 22, 2019 at 02:43:15PM -0400, Sasha Levin wrote:
> > > > From: Austin Kim <austindh.kim@xxxxxxxxx>
> > > >
> > > > [ Upstream commit 864b23f0169d5bff677e8443a7a90dfd6b090afc ]
> > > >
> > > > The result of kmalloc() should have been checked ahead of below statement:
> > > >
> > > > 	pqp = (struct bau_pq_entry *)vp;
> > > >
> > > > Move BUG_ON(!vp) before above statement.
> > > >
> > > > Signed-off-by: Austin Kim <austindh.kim@xxxxxxxxx>
> ...
> > > > ---
> > > >   arch/x86/platform/uv/tlb_uv.c | 4 ++--
> > > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
> > > > index 20c389a91b803..5f0a96bf27a1f 100644
> > > > --- a/arch/x86/platform/uv/tlb_uv.c
> > > > +++ b/arch/x86/platform/uv/tlb_uv.c
> > > > @@ -1804,9 +1804,9 @@ static void pq_init(int node, int pnode)
> > > >
> > > >   	plsize = (DEST_Q_SIZE + 1) * sizeof(struct bau_pq_entry);
> > > >   	vp = kmalloc_node(plsize, GFP_KERNEL, node);
> > > > -	pqp = (struct bau_pq_entry *)vp;
> > > > -	BUG_ON(!pqp);
> > > > +	BUG_ON(!vp);
> > > >
> > > > +	pqp = (struct bau_pq_entry *)vp;
> > > >   	cp = (char *)pqp + 31;
> > > >   	pqp = (struct bau_pq_entry *)(((unsigned long)cp >> 5) << 5);
> > >
> > > How did this even get merged in the first place?  I thought a number of
> > > us complained about it.
> > >
> > > This isn't any change in code, and the original is just fine, the author
> > > didn't realize how C works :(
>
> Mind you, the code itself if pretty horrid.
> Looks like it is aligning to 32 bytes, easier done by:
> 	pqp = (void *)((unsigned long)vp + 31 & ~31);
> (and there's a roundup macro to obfuscate it somewhere.)
> But I'd also expect to see a matching '+ 31' in the size passed to kmalloc().
> Not to mention a comment!
>
> 	David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)

Thanks, I will put all of these comments in my notes.  This whole 
function is slated to move to a specialized UV APIC driver since it uses 
a unique scaling feature available in the UV hardware.  (The original 
author has long retired.)

-Mike