Re: [PATCH net 1/7] secure_seq: return the full 64-bit of the siphash

From: Willy Tarreau <w@1wt.eu>
To: kernel test robot <lkp@intel.com>
Cc: netdev@vger.kernel.org, kbuild-all@lists.01.org,
	Jakub Kicinski <kuba@kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	Moshe Kol <moshe.kol@mail.huji.ac.il>,
	Yossi Gilad <yossi.gilad@mail.huji.ac.il>,
	Amit Klein <aksecurity@gmail.com>,
	linux-kernel@vger.kernel.org,
	"Jason A . Donenfeld" <Jason@zx2c4.com>
Subject: Re: [PATCH net 1/7] secure_seq: return the full 64-bit of the siphash
Date: Wed, 27 Apr 2022 18:35:54 +0200	[thread overview]
Message-ID: <20220427163554.GA3746@1wt.eu> (raw)
In-Reply-To: <20220427100714.GC1724@1wt.eu>

On Wed, Apr 27, 2022 at 12:07:14PM +0200, Willy Tarreau wrote:
> On Wed, Apr 27, 2022 at 05:56:41PM +0800, kernel test robot wrote:
> > Hi Willy,
> > 
> > I love your patch! Yet something to improve:
> > 
> > [auto build test ERROR on net/master]
> > 
> > url:    https://github.com/intel-lab-lkp/linux/commits/Willy-Tarreau/insufficient-TCP-source-port-randomness/20220427-145651
> > base:   https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git 71cffebf6358a7f5031f5b208bbdc1cb4db6e539
> > config: i386-randconfig-r026-20220425 (https://download.01.org/0day-ci/archive/20220427/202204271705.VrWNPv7n-lkp@intel.com/config)
> > compiler: gcc-11 (Debian 11.2.0-20) 11.2.0
> > reproduce (this is a W=1 build):
> >         # https://github.com/intel-lab-lkp/linux/commit/01b26e522b598adf346b809075880feab3dcdc08
> >         git remote add linux-review https://github.com/intel-lab-lkp/linux
> >         git fetch --no-tags linux-review Willy-Tarreau/insufficient-TCP-source-port-randomness/20220427-145651
> >         git checkout 01b26e522b598adf346b809075880feab3dcdc08
> >         # save the config file
> >         mkdir build_dir && cp config build_dir/.config
> >         make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
> > 
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@intel.com>
> > 
> > All errors (new ones prefixed by >>):
> > 
> >    ld: net/ipv4/inet_hashtables.o: in function `__inet_hash_connect':
> > >> inet_hashtables.c:(.text+0x187d): undefined reference to `__umoddi3'
> 
> Argh! indeed, we spoke about using div_u64_rem() at the beginning and
> that one vanished over time. Will respin it.

I fixed it, built it for i386 and x86_64, tested it on x86_64 and confirmed
that it still does what I need. The change is only this:

-       offset = (READ_ONCE(table_perturb[index]) + (port_offset >> 32)) % remaining;
+       div_u64_rem(READ_ONCE(table_perturb[index]) + (port_offset >> 32), remaining, &offset);

I'll send a v2 series in a few hours if there are no more comments.

Willy