linux-kernel - [PATCH 3/3] netfilter: xt_hashlimit: uses div

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Message-Id: <20160930160559.4102745-3-arnd@arndb.de>
Date:   Fri, 30 Sep 2016 18:05:36 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Patrick McHardy <kaber@...sh.net>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        "David S. Miller" <davem@...emloft.net>,
        Joshua Hunt <johunt@...mai.com>,
        Vishwanath Pai <vpai@...mai.com>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] netfilter: xt_hashlimit: uses div_u64 for division

The newly added support for high-resolution pps rates introduced multiple 64-bit
division operations in one function, which fails on all 32-bit architectures:

net/netfilter/xt_hashlimit.o: In function `user2credits':
xt_hashlimit.c:(.text.user2credits+0x3c): undefined reference to `__aeabi_uldivmod'
xt_hashlimit.c:(.text.user2credits+0x68): undefined reference to `__aeabi_uldivmod'
xt_hashlimit.c:(.text.user2credits+0x88): undefined reference to `__aeabi_uldivmod'

This replaces the division with an explicit call to div_u64 for version 2
to documents that this is a slow operation, and reverts back to 32-bit arguments
for the version 1 data to restore the original faster 32-bit division.

With both changes combined, we no longer get a link error.

Fixes: 11d5f15723c9 ("netfilter: xt_hashlimit: Create revision 2 to support higher pps rates")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
Vishwanath Pai already sent a patch for this, and I did my version independently.
The difference is that his version also the more expensive division for the
version 1 variant that doesn't need it.

See also http://patchwork.ozlabs.org/patch/676713/
---
 net/netfilter/xt_hashlimit.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 44a095ecc7b7..3d5525df6eb3 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -464,20 +464,23 @@ static u32 xt_hashlimit_len_to_chunks(u32 len)
 static u64 user2credits(u64 user, int revision)
 {
 	if (revision == 1) {
+		u32 user32 = user; /* use 32-bit division */
+
 		/* If multiplying would overflow... */
-		if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY_v1))
+		if (user32 > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY_v1))
 			/* Divide first. */
-			return (user / XT_HASHLIMIT_SCALE) *\
+			return (user32 / XT_HASHLIMIT_SCALE) *
 						HZ * CREDITS_PER_JIFFY_v1;
 
-		return (user * HZ * CREDITS_PER_JIFFY_v1) \
-						/ XT_HASHLIMIT_SCALE;
+		return (user32 * HZ * CREDITS_PER_JIFFY_v1) /
+						XT_HASHLIMIT_SCALE;
 	} else {
 		if (user > 0xFFFFFFFFFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
-			return (user / XT_HASHLIMIT_SCALE_v2) *\
-						HZ * CREDITS_PER_JIFFY;
+			return div_u64_u64(user, XT_HASHLIMIT_SCALE_v2) *
+					   HZ * CREDITS_PER_JIFFY;
 
-		return (user * HZ * CREDITS_PER_JIFFY) / XT_HASHLIMIT_SCALE_v2;
+		return div_u64_u64(user * HZ * CREDITS_PER_JIFFY,
+				   XT_HASHLIMIT_SCALE_v2);
 	}
 }
 
-- 
2.9.0