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 5370E38E8BE for ; Tue, 7 Jul 2026 09:54:23 +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=1783418065; cv=none; b=PNDqvcI/Bx85mGfwJ2L15poXHflfvY+XESMIqiSYyy8epLg9fTzLyDII7hdRNJwjsI++80EJW9fIqT4s4WA5myGxogMvVLWb1S+Djd6Zg+b3voqennm3jWL2OceBMQ/qIkqKCvI6QWyLEng04Q8jdTjQmD+mY7trMJu7F3hv33E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783418065; c=relaxed/simple; bh=1RPbrznEBE+sD/+GrGn9+v1fT4NtGyvxz3LtOgdlKNs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FIdTrmB9W8BnOxp6mDgat25CSZkixEhtj28lgiBl4xWw/xnh2KeSllVeMeu0W0kaqtDO+HmOZ5bIpV9jQLO1orgm4dBRlO6dREODffm2qGzsPWBqs+VmKg3Wi9n1v9ufL58vLJu2r97a7f4FbShgRaFWuo+56Nlr6JLIwyRkT8U= 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=fNIdHyjY; 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="fNIdHyjY" 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 16A731BB0; Tue, 7 Jul 2026 02:54:18 -0700 (PDT) Received: from e129823.arm.com (e129823.arm.com [10.2.213.3]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 17E623F7B4; Tue, 7 Jul 2026 02:54:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1783418062; bh=1RPbrznEBE+sD/+GrGn9+v1fT4NtGyvxz3LtOgdlKNs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fNIdHyjYmKheS0FfTbOb56Q/Ijbw2c8lkdwVEK8ZdeQ9aiivcjnGxda7Gx48wTtzJ 9Ly0VJ53djJ7XK75P5HpIpCwBtBVV5uNTXxEDZfkgkVsrCqTjhi9i5yJ/Qcvt0R9pb 8hC0vSd0faz73mBAF4PmITC5/ouy7C/OkGlagSWA= Date: Tue, 7 Jul 2026 10:54:18 +0100 From: Yeoreum Yun To: Leo Yan 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 v8 08/13] coresight: etm4x: fix inconsistencies with sysfs configuration Message-ID: References: <20260629090007.1718746-1-yeoreum.yun@arm.com> <20260629090007.1718746-9-yeoreum.yun@arm.com> <20260706172159.GA1024232@e132581.arm.com> <20260707082510.GD1024232@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, Jul 07, 2026 at 09:59:36AM +0100, Yeoreum Yun wrote: > On Tue, Jul 07, 2026 at 09:25:10AM +0100, Leo Yan wrote: > > On Mon, Jul 06, 2026 at 07:16:42PM +0100, Yeoreum Yun wrote: > > > > [...] > > > > > > I try best to not paste any non-sense AI reviews, record one from > > > > Sashiko [1]: > > > > > > > > | If a user writes to a sysfs attribute like pe_sel_store(), it acquires > > > > | drvdata->spinlock without disabling interrupts. If an IPI is then handled > > > > | on the same CPU, etm4_enable_sysfs_smp_call() will call > > > > | cscfg_csdev_enable_active_config() which attempts to acquire the exact > > > > | same spinlock, hanging the CPU." > > > > > > > > The flow for acquiring drvdata->spinlock in SMP call is: > > > > > > > > etm4_enable_sysfs_smp_call() > > > > `> cscfg_csdev_enable_active_config() > > > > `> cscfg_csdev_enable_config() > > > > `> cscfg_prog_config() > > > > `> cscfg_set_on_enable() > > > > `> raw_spin_lock_irqsave(feat_csdev->drv_spinlock, flags); > > > > > > > > We might expect the complaint from LOCKDEP with this patch. > > > > > > Hmm. I miss the this point and there is two solution: > > > > > > 1. Remove "feat_csdev->drv_spinlock" > > > > > > Before this patch, the "feat_csdev->drv_spinlock" is for > > > synchronizing with the "drvdata->config". However, > > > After this patch, the the configfs only show the "active" config > > > and the active config can be used only after taking the "mode". > > > > > > Furthermore, the sysfs only uses the "config" not "active config", > > > there is no race between the sysfs and the configfs. > > > > > > When I check the, "feat_csdev->drv_spinlock" is for the > > > active/deactive the configfs config, so I seems safe to remove. > > > > My interpretation is: > > > > After this series, we updates active_config on local CPU within atomic > > context, it is nature to be protected. So we don't need to use > > feat_csdev->drv_spinlock when updating active_config. > > > > If so, it is fine for me to remove feat_csdev->drv_spinlock. > > Yes. but if I add a little bit more comment. the "active_config" > is accessed after "mode changed (perf of sysfs)" it accesses atomically > and the "active_config" is refered from the configfs not "config" > after this patch. So we can remove the "feat_csdev->drv_spinlock". > > > > > > 2. sysfs with _irqsave? > > > > > > However, this make a latency for the sysfs. > > > > > > I think the (1) seems good. > > > > > > Any comments? @Suzuki and @Leo? > > > > Yeah, it is good to wait a bit for Suzuki if any ideas. > > Okay. If he doesn't have any particular comment, I'll send with next > version. Just for clarification, I'll not remove the drv_spinlock field from cscfg_feature_csdev but to set this field as NULL for etm4 and still make a irqsave/restore in the cscfg_set_on_enable/disable(). Thanks! -- Sincerely, Yeoreum Yun