Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753881AbbBYQMC (ORCPT ); Wed, 25 Feb 2015 11:12:02 -0500 Received: from mail-vc0-f173.google.com ([209.85.220.173]:64419 "EHLO mail-vc0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753824AbbBYQL7 (ORCPT ); Wed, 25 Feb 2015 11:11:59 -0500 MIME-Version: 1.0 In-Reply-To: <3465519.0ga9zC7F7b@wuerfel> References: <1424878581-11701-1-git-send-email-bobby.prani@gmail.com> <3465519.0ga9zC7F7b@wuerfel> From: Pranith Kumar Date: Wed, 25 Feb 2015 11:11:28 -0500 Message-ID: Subject: Re: [RFC PATCH] arm: asm/cmpxchg.h: Add support half-word xchg() To: Arnd Bergmann Cc: "moderated list:ARM PORT" , Russell King , open list Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3019 Lines: 74 On Wed, Feb 25, 2015 at 10:58 AM, Arnd Bergmann wrote: > On Wednesday 25 February 2015 10:36:20 Pranith Kumar wrote: >> This patch adds support for a half-word xchg() for ARM using ldrexh/strexh >> instructions. It also fixes an asm comment for __cmpxchg2. >> >> Currently using a half-word xchg() results in the following splat on an ARMv7 >> machine. >> >> [ 45.833303] xchg: bad data size: pc 0xbe806020, ptr 0xeb18deee, size 2 >> [ 45.833324] ------------[ cut here ]------------ >> [ 45.837939] kernel BUG at /dvs/git/dirty/git-master_linux/kernel/arch/arm/kernel/traps.c:727! >> >> Signed-off-by: Pranith Kumar > > Unfortunately, the BUG message seems incomplete, can you reproduce this > with CONFIG_DEBUG_BUGVERBOSE enabled? The bug here is in a module caused when xchg() was used on uint16_t variable. It is caused by the __bad_xchg() for 2 byte swap. More information: [ 45.833303] xchg: bad data size: pc 0xbe806020, ptr 0xeb18deee, size 2 [ 45.833324] ------------[ cut here ]------------ [ 45.837939] kernel BUG at /dvs/git/dirty/git-master_linux/kernel/arch/arm/kernel/traps.c:727! [ 45.846450] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM [ 45.852275] Modules linked in: test(O+) nvhost_vi [ 45.857012] CPU: 0 PID: 1848 Comm: insmod Tainted: G O 3.10.24-g6a2d13a #1 [ 45.864744] task: ee406580 ti: eb18c000 task.ti: eb18c000 [ 45.870141] PC is at __bad_xchg+0x24/0x28 [ 45.874146] LR is at __bad_xchg+0x24/0x28 > >> arch/arm/include/asm/cmpxchg.h | 18 +++++++++++++++++- >> 1 file changed, 17 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h >> index abb2c37..9505cca 100644 >> --- a/arch/arm/include/asm/cmpxchg.h >> +++ b/arch/arm/include/asm/cmpxchg.h >> @@ -50,6 +50,16 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size >> : "r" (x), "r" (ptr) >> : "memory", "cc"); >> break; >> + case 2: >> + asm volatile("@ __xchg2\n" >> + "1: ldrexh %0, [%3]\n" >> + " strexh %1, %2, [%3]\n" >> + " teq %1, #0\n" >> + " bne 1b" >> + : "=&r" (ret), "=&r" (tmp) >> + : "r" (x), "r" (ptr) >> + : "memory", "cc"); >> + break; >> case 4: >> asm volatile("@ __xchg4\n" >> "1: ldrex %0, [%3]\n" > > Does this work on all ARMv6 or just ARMv6k? > ldrexh/strexh is being used in cmpxchg() in the same file in a similar manner, and the comment there says that it works for all ARCH >= ARMv6k, so not ARMv6 I guess. -- Pranith -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/