From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 6D3612417D9 for ; Tue, 21 Apr 2026 13:28:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776778127; cv=none; b=dv6S+AOmenxyJ9FqB/H8pO5LUfHn2rYoGHuFOmKhRohMqSbTgVqEO6NEfDTJDEqynC2dW0TT/ZVpkyoW8YFaaQGM6JuPVsvHaWp+FhgJwmkAUJ8bqZmuyQlU1Q4Ss/hoMeLNNZ+n9Z9Wrbizp9LPMeeZAaFORaXp6Jx2DV/PSFQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776778127; c=relaxed/simple; bh=+1X+DlknRjHqKgv3dA+1G8Jnl/AycFThXqT8ZxAXDzE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=e777nq6bLfvjU624rK8xK7ZvG55pfVpsAcoWjZDfnoktRGeG7J5E86ZuXiQKfFP2hE1WrFqXYcC8LuukgkS5+q3jkbIqP3OWf/L6f0obi6oBJdZdBPqo6dRC5hQ+vYj074MT9mGbakuzL1bXc1EzYFvNRI5w2G7Aehs7h4LzTp0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=X2BriHx/; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="X2BriHx/" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 37D2C1BF3; Tue, 21 Apr 2026 06:28:40 -0700 (PDT) Received: from localhost (e132581.arm.com [10.1.196.87]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4A7E43FE87; Tue, 21 Apr 2026 06:28:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1776778125; bh=+1X+DlknRjHqKgv3dA+1G8Jnl/AycFThXqT8ZxAXDzE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=X2BriHx/r5DzNtTFzlzG4r9GRVY4hpopEZb83uwmv6QTY6f5ROZgn5z/IJSIZgamE fvCWoYzFk3Yj69WcE5oa8JuNBTS8BII0Xe02ELOtqQufyToSXjtSK6NTRaN7rqjiWk jBmZdtzSTeYiNnKbxpmDChAf0pQ+btlzvzXGyvVo= Date: Tue, 21 Apr 2026 14:28:42 +0100 From: Leo Yan To: Yeoreum Yun Cc: coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, suzuki.poulose@arm.com, mike.leach@arm.com, james.clark@linaro.org, alexander.shishkin@linux.intel.com, jie.gan@oss.qualcomm.com Subject: Re: [PATCH v5 07/12] coresight: etm4x: fix inconsistencies with sysfs configuration Message-ID: <20260421132842.GC929984@e132581.arm.com> References: <20260415165528.3369607-1-yeoreum.yun@arm.com> <20260415165528.3369607-8-yeoreum.yun@arm.com> <20260421104601.GB929984@e132581.arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Apr 21, 2026 at 12:14:20PM +0100, Yeoreum Yun wrote: [...] > > > - There is a risk of corrupting drvdata->config if a perf session enables > > > tracing while cscfg_csdev_disable_active_config() is being handled in > > > etm4_disable_sysfs(). > > > > Similiar to above, cscfg_csdev_disable_active_config() is not > > protected in etm4_disable_sysfs(). > > This is not true. > at the time of etm4_disable_sysfs() "mode" is already taken > (whether sysfs or perf). In this situation, it's enough to > call cscfg_csdev_disable_active_config() before chaning > mode to DISABLED. To be clear, I am trying to understand issue _before_ your patch. Without this patch, cscfg_csdev_disable_active_config() is not protected by the mode. > > > struct etm4_enable_arg { > > > struct etmv4_drvdata *drvdata; > > > + struct etmv4_config config; > > > > We don't need this. We can defer to get drvdata->config in SMP call. > > This is not true ane make a situation more complex. > If we get config in SMP call, that would be a problem when some user is > trying to modify config. > > IOW, while user modifying config via sysfs, and SMP call happens, > it makes a dead lock. so for this if we try to grab the lock in SMP call, > we should change every sysfs raw_spin_lock() into raw_spin_lock_irqsave(). > > Instead of this it would be much clear and simpler to get config in here > rather than to add some latencies via sysfs. Thanks for info. If so, it is fine for me to add "config". > > > @@ -1386,6 +1401,7 @@ static void etm4_init_arch_data(void *info) > > > drvdata = dev_get_drvdata(init_arg->dev); > > > caps = &drvdata->caps; > > > csa = init_arg->csa; > > > + config = &drvdata->active_config; > > > > Should we init drvdata->config instead so make it has sane values ? > > > > In other words, drvdata->active_config are always set at the runtime, > > so don't need to init it at all, right? > > No. at least when the initialise, I think we should fill the its > contesnt with the "etm4_set_default()". > > That's why the consequence call etm4_set_default() called with > active_config and config is coped with the default configutation. I'm concerned that some config fields may be reused across sessions. For example, a sysfs session copies drvdata->config into drvdata->active_config, and later a perf session may reuse stale values. The same issue can happen in the reverse direction. A clean approach would be to treat drvdata->active_config as per-session state: 1) clear drvdata->active_config at session start 2) apply the session-specific config 2.1) sysfs: use drvdata->config 2.2) perf: use event config 3) then apply configfs configuration So we should clear drvdata->active_config at the start of each session and rebuild it with the correct configuration. Thanks, Leo