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[2001:4830:134:3::11]) by mx.google.com with ESMTPS id e9si22457495qhc.1.2016.04.04.07.36.44 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 04 Apr 2016 07:36:44 -0700 (PDT) Received-SPF: pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 2001:4830:134:3::11 as permitted sender) client-ip=2001:4830:134:3::11; Authentication-Results: mx.google.com; dkim=fail header.i=@linaro.org; spf=pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 2001:4830:134:3::11 as permitted sender) smtp.mailfrom=qemu-devel-bounces+patch=linaro.org@nongnu.org; dmarc=fail (p=NONE dis=NONE) header.from=linaro.org Received: from localhost ([::1]:59016 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1an5cR-0006AK-T3 for patch@linaro.org; Mon, 04 Apr 2016 10:36:43 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43327) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1an5bj-0005V7-Fi for qemu-devel@nongnu.org; Mon, 04 Apr 2016 10:36:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1an5bd-0004Bc-DV for qemu-devel@nongnu.org; Mon, 04 Apr 2016 10:35:59 -0400 Received: from mail-lf0-x236.google.com ([2a00:1450:4010:c07::236]:36710) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1an5bd-0004BW-2t for qemu-devel@nongnu.org; Mon, 04 Apr 2016 10:35:53 -0400 Received: by mail-lf0-x236.google.com with SMTP id g184so99290639lfb.3 for ; Mon, 04 Apr 2016 07:35:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=HW/LKGLyeml8Kr3hLNTDEcXy1obPf8uTvAKYAL9nN6U=; b=ApW+uExXzHWCK0Ypt50F+0TgE1bg/AWdbau9DLJbZrnEq4DrCIZdLTX5yP0sz2Pt+7 OQiHWgpT7SSQ5m+bfCc2OzfWaMq/9N7CB4jq9FxFsvag0n3DE2h22qAWx7KtS/++INau +NnfcvWN7r/XhtUMgVarbx/FTLOLxzxlo8kME= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=HW/LKGLyeml8Kr3hLNTDEcXy1obPf8uTvAKYAL9nN6U=; b=f+ImJPiFPHB7De7e3yOHC1lsepZDoa1J+S25BNwDby0Z3W7ZS45Oq2kfj6Sx5AGxR3 1PhSIDbgQP4KH7MwXGe2PG7rxOkz62iZMlJJIGxiG0t+0gbPBH4L/s9vjYaJJbeHkbDv 2nFbmuyF6SbNVgsOEeaYBfZ5NxBIjCt03e1vkNeng0LJ6FmY+g9ixWMySpbFg21qH/nZ TG2blofiqeiKyZTH7or4+BoKxJtf9fio27cYQrYzvXa8d4fm4DHYpX2rHT6XRS698qp9 Fdqg4e/yVctJ8l2XGnIhW7IOgpWkd1frjBw9914d8dsjr93DY1lpB+5Wgs72QS0Jemog OM4Q== X-Gm-Message-State: AD7BkJKaofcdhPIcuKa6xbuHIOc1EdNEbmmgROgmBTt6IqTcCNP7aGAbjxVs0giJo+35N8LC X-Received: by 10.28.16.141 with SMTP id 135mr12613275wmq.67.1459780552090; Mon, 04 Apr 2016 07:35:52 -0700 (PDT) Received: from zen.linaro.local ([81.128.185.34]) by smtp.gmail.com with ESMTPSA id ka7sm29397999wjb.8.2016.04.04.07.35.50 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 04 Apr 2016 07:35:51 -0700 (PDT) Received: from zen.linaroharston (localhost [127.0.0.1]) by zen.linaro.local (Postfix) with ESMTP id 61BEE3E0932; Mon, 4 Apr 2016 15:35:51 +0100 (BST) From: =?UTF-8?q?Alex=20Benn=C3=A9e?= To: peter.maydell@linaro.org Date: Mon, 4 Apr 2016 15:35:48 +0100 Message-Id: <1459780549-12942-2-git-send-email-alex.bennee@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1459780549-12942-1-git-send-email-alex.bennee@linaro.org> References: <1459780549-12942-1-git-send-email-alex.bennee@linaro.org> MIME-Version: 1.0 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2a00:1450:4010:c07::236 Cc: Peter Crosthwaite , qemu-devel@nongnu.org, sbruno@freebsd.org, pbonzini@redhat.com, =?UTF-8?q?Alex=20Benn=C3=A9e?= , Richard Henderson Subject: [Qemu-devel] [PATCH v2 1/2] cpus: don't use atomic_read for vm_clock_warp_start X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org As vm_clock_warp_start is a 64 bit value this causes problems for the compiler trying to come up with a suitable atomic operation on 32 bit hosts. Because the variable is protected by vm_clock_seqlock, we check its value inside a seqlock critical section. Signed-off-by: Alex Bennée --- v2 - use seqlock read instead wrapping inside the write sequence lock --- cpus.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) -- 2.7.4 diff --git a/cpus.c b/cpus.c index 8ae4777..cbeb1f6 100644 --- a/cpus.c +++ b/cpus.c @@ -338,10 +338,18 @@ static int64_t qemu_icount_round(int64_t count) static void icount_warp_rt(void) { + unsigned seq; + int64_t warp_start; + /* The icount_warp_timer is rescheduled soon after vm_clock_warp_start * changes from -1 to another value, so the race here is okay. */ - if (atomic_read(&vm_clock_warp_start) == -1) { + do { + seq = seqlock_read_begin(&timers_state.vm_clock_seqlock); + warp_start = vm_clock_warp_start; + } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, seq)); + + if (warp_start == -1) { return; }