Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754366Ab0KWSf1 (ORCPT ); Tue, 23 Nov 2010 13:35:27 -0500 Received: from [69.28.251.93] ([69.28.251.93]:36795 "EHLO b32.net" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751603Ab0KWSf0 (ORCPT ); Tue, 23 Nov 2010 13:35:26 -0500 From: Kevin Cernekee To: Ralf Baechle Cc: , Subject: [PATCH 6/7] MIPS: Fix CP0 COUNTER clockevent race Date: Tue, 23 Nov 2010 10:26:44 -0800 Message-Id: <444ef6c4bbb47d55c700452d8cd23229@localhost> In-Reply-To: <8a8eee995454c8b271cceb440e31699a@localhost> References: <8a8eee995454c8b271cceb440e31699a@localhost> User-Agent: vim 7.2 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1474 Lines: 41 Consider the following test case: write_c0_compare(read_c0_count()); Even if the counter doesn't increment during execution, this might not generate an interrupt until the counter wraps around. The CPU may perform the comparison each time CP0 COUNT increments, not when CP0 COMPARE is written. If mips_next_event() is called with a very small delta, and CP0 COUNT increments during the calculation of "cnt += delta", it is possible that CP0 COMPARE will be written with the current value of CP0 COUNT. If this is detected, the function should return -ETIME, to indicate that the interrupt might not have actually gotten scheduled. Signed-off-by: Kevin Cernekee --- arch/mips/kernel/cevt-r4k.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/arch/mips/kernel/cevt-r4k.c b/arch/mips/kernel/cevt-r4k.c index 2f4d7a9..98c5a97 100644 --- a/arch/mips/kernel/cevt-r4k.c +++ b/arch/mips/kernel/cevt-r4k.c @@ -32,7 +32,7 @@ static int mips_next_event(unsigned long delta, cnt = read_c0_count(); cnt += delta; write_c0_compare(cnt); - res = ((int)(read_c0_count() - cnt) > 0) ? -ETIME : 0; + res = ((int)(read_c0_count() - cnt) >= 0) ? -ETIME : 0; return res; } -- 1.7.0.4 -- 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/