From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vishwanath Pai Subject: Re: [PATCH] netfilter: xt_hashlimit: avoid 64-bit division Date: Wed, 6 Sep 2017 16:22:30 -0400 Message-ID: <7791dee1-64a9-dcaa-c5d9-0b04a44bc526@akamai.com> References: <20170906195825.3715290-1-arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Josh Hunt , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Arnd Bergmann , Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal , "David S. Miller" Return-path: In-Reply-To: <20170906195825.3715290-1-arnd@arndb.de> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 09/06/2017 03:57 PM, Arnd Bergmann wrote: > 64-bit division is expensive on 32-bit architectures, and > requires a special function call to avoid a link error like: > > net/netfilter/xt_hashlimit.o: In function `hashlimit_mt_common': > xt_hashlimit.c:(.text+0x1328): undefined reference to `__aeabi_uldivmod' > > In the case of hashlimit_mt_common, we don't actually need a > 64-bit operation, we can simply rewrite the function slightly > to make that clear to the compiler. > > Fixes: bea74641e378 ("netfilter: xt_hashlimit: add rate match mode") > Signed-off-by: Arnd Bergmann > --- > net/netfilter/xt_hashlimit.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c > index 10d48234f5f4..50b53d86eef5 100644 > --- a/net/netfilter/xt_hashlimit.c > +++ b/net/netfilter/xt_hashlimit.c > @@ -531,7 +531,10 @@ static u64 user2rate_bytes(u64 user) > { > u64 r; > > - r = user ? 0xFFFFFFFFULL / user : 0xFFFFFFFFULL; > + if (user > 0xFFFFFFFFULL) > + return 0; > + > + r = user ? 0xFFFFFFFFULL / (u32)user : 0xFFFFFFFFULL; > r = (r - 1) << 4; > return r; > } > I have submitted another patch to fix this: https://patchwork.ozlabs.org/patch/809881/ We have seen this problem before, I was careful not to introduce this again in the new patch but clearly I overlooked this particular line :( In the other cases we fixed it by replacing division with div64_u64(). -Vishwanath