From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CE1EAFD8766 for ; Tue, 17 Mar 2026 13:07:36 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 6185F10E627; Tue, 17 Mar 2026 13:07:36 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="CVG15I82"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.7]) by gabe.freedesktop.org (Postfix) with ESMTPS id 0C20410E62A for ; Tue, 17 Mar 2026 13:07:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1773752855; x=1805288855; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version:content-transfer-encoding; bh=F0p8gQPBLZEVD9EM+ov7iJ+l8edm5JCED+CAd61J5VY=; b=CVG15I82RMwv8pIm3cgAxNlM1n6XVEDLK40T7EZ0+Oe4kH2AXtR32pGc 0pd9JbOOrscNq4sg7s5MzMVsWnZDqQ+GsoMmU59vGf2fHPYjMBv7RN17B o/udm53J2Gc4NI+rlV9dqYpJGx/fz37s0RIHX+qpozw2hVahrFK7hJENX o5PpN67eMuZoqr5v3RDnFOmv1vx7cNhgrP4bhq/hU2AEa4rjs6jeNVLN7 HvubqjSv1zncT0REvRYc4Bcz3V1WrTQpF0aZahObpXoFZIJJKdx/fwMXN QL/oAOjxxA6ntcajWz/kd8jgWyHQH8PgytKRoCYyE/llWta8zYY3KN18r A==; X-CSE-ConnectionGUID: 2+gcr/UIQnG85R708LeNBQ== X-CSE-MsgGUID: Jv9bUpN5SGuu3dOxYuAydQ== X-IronPort-AV: E=McAfee;i="6800,10657,11732"; a="100239769" X-IronPort-AV: E=Sophos;i="6.23,124,1770624000"; d="scan'208";a="100239769" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Mar 2026 06:07:34 -0700 X-CSE-ConnectionGUID: AvYKnYs2SLSTsTIkPNxv/w== X-CSE-MsgGUID: f3iVZsrJQFiedHUOLmFoDg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,124,1770624000"; d="scan'208";a="217963748" Received: from krybak-mobl1.ger.corp.intel.com (HELO localhost) ([10.245.246.32]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Mar 2026 06:07:32 -0700 From: Jani Nikula To: Ville Syrjala , intel-gfx@lists.freedesktop.org Cc: stable@vger.kernel.org Subject: Re: [PATCH] drm/i915: Order OP vs. timeout correctly in __wait_for() In-Reply-To: <20260313110740.24620-1-ville.syrjala@linux.intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - c/o Alberga Business Park, 6 krs Bertel Jungin Aukio 5, 02600 Espoo, Finland References: <20260313110740.24620-1-ville.syrjala@linux.intel.com> Date: Tue, 17 Mar 2026 15:07:29 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Fri, 13 Mar 2026, Ville Syrjala wrote: > From: Ville Syrj=C3=A4l=C3=A4 > > Put the barrier() before the OP so that anything we read out in > OP and check in COND will actually be read out after the timeout > has been evaluated. > > Currently the only place where we use OP is __intel_wait_for_register(), > but the use there is precisely susceptible to this reordering, assuming > the ktime_*() stuff itself doesn't act as a sufficient barrier: > > __intel_wait_for_register(...) > { > ... > ret =3D __wait_for(reg_value =3D intel_uncore_read_notrace(...), > (reg_value & mask) =3D=3D value, ...); > ... > } > > Cc: stable@vger.kernel.org > Fixes: 1c3c1dc66a96 ("drm/i915: Add compiler barrier to wait_for") > Signed-off-by: Ville Syrj=C3=A4l=C3=A4 Reviewed-by: Jani Nikula > --- > drivers/gpu/drm/i915/i915_wait_util.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/i915_wait_util.h b/drivers/gpu/drm/i915= /i915_wait_util.h > index 7376898e3bf8..e1ed7921ec70 100644 > --- a/drivers/gpu/drm/i915/i915_wait_util.h > +++ b/drivers/gpu/drm/i915/i915_wait_util.h > @@ -25,9 +25,9 @@ > might_sleep(); \ > for (;;) { \ > const bool expired__ =3D ktime_after(ktime_get_raw(), end__); \ > - OP; \ > /* Guarantee COND check prior to timeout */ \ > barrier(); \ > + OP; \ > if (COND) { \ > ret__ =3D 0; \ > break; \ --=20 Jani Nikula, Intel