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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0A991C433F5 for ; Tue, 30 Nov 2021 12:05:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241311AbhK3MIo (ORCPT ); Tue, 30 Nov 2021 07:08:44 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:48450 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241281AbhK3MIj (ORCPT ); Tue, 30 Nov 2021 07:08:39 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 8146BB81846; Tue, 30 Nov 2021 12:05:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 940D1C53FCF; Tue, 30 Nov 2021 12:05:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638273915; bh=BKaO6kLYHyi6gZ59PeSbDaTBZNbumFvE8rNJV7KzBlo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hOF11PwF8K02hkwjdiO7NNATq3dgnUdSInx6jH8I2MQrgB14tcs6k1ABlD5nF09Kk YQevQKXR/0LMspeXSihyjYp+weSiCKaNtt2SYK7aEaSYk6rApaJ6x4M3JRTDejckk9 0TSBp31MYGDXStoZhwTz/J1PfdJzZsnallQrkqLRsF8KRy5N3zeMxK1SgTgF8OzAJ/ 0IkmYPur0X91lab3GZ/relF9o28mWTSdSO2/0wnmTjFuwCmIRXA4HiUq2AARUA28q1 ZA4MjzIiazd1BYwA07/g5ALL77md8TEcC2jkNCZxDifGIWT80v/UW/bQ6fhZbx2lmV nKwBMfWClWjLw== Date: Tue, 30 Nov 2021 13:05:11 +0100 From: Frederic Weisbecker To: Nicolas Saenz Julienne Cc: linux-kernel , linux-arm-kernel , rcu@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Mark Rutland , Steven Rostedt , paulmck@kernel.org, mtosatti Subject: Re: Question WRT early IRQ/NMI entry code Message-ID: <20211130120511.GB599355@lothringen> References: <8719ad46cc29a2c5d7baac3c35770e5460ab8d5c.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8719ad46cc29a2c5d7baac3c35770e5460ab8d5c.camel@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 30, 2021 at 12:28:41PM +0100, Nicolas Saenz Julienne wrote: > Hi All, > while going over the IRQ/NMI entry code I've found a small 'inconsistency': > while in the IRQ entry path, we inform RCU of the context change *before* > incrementing the preempt counter, the opposite happens for the NMI entry > path. This applies to both arm64 and x86[1]. > > Actually, rcu_nmi_enter() — which is also the main RCU context switch function > for the IRQ entry path — uses the preempt counter to verify it's not in NMI > context. So it would make sense to assume all callers have the same updated > view of the preempt count, which isn't true ATM. > > I'm sure there an obscure/non-obvious reason for this, right? At least I can't find an immediate reason for it either :-) Thanks! 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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ms1t0-0050KR-Fv; Tue, 30 Nov 2021 12:05:26 +0000 Received: from sin.source.kernel.org ([2604:1380:40e1:4800::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1ms1st-0050Fk-KZ for linux-arm-kernel@lists.infradead.org; Tue, 30 Nov 2021 12:05:21 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 07E69CE18BE; Tue, 30 Nov 2021 12:05:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 940D1C53FCF; Tue, 30 Nov 2021 12:05:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638273915; bh=BKaO6kLYHyi6gZ59PeSbDaTBZNbumFvE8rNJV7KzBlo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hOF11PwF8K02hkwjdiO7NNATq3dgnUdSInx6jH8I2MQrgB14tcs6k1ABlD5nF09Kk YQevQKXR/0LMspeXSihyjYp+weSiCKaNtt2SYK7aEaSYk6rApaJ6x4M3JRTDejckk9 0TSBp31MYGDXStoZhwTz/J1PfdJzZsnallQrkqLRsF8KRy5N3zeMxK1SgTgF8OzAJ/ 0IkmYPur0X91lab3GZ/relF9o28mWTSdSO2/0wnmTjFuwCmIRXA4HiUq2AARUA28q1 ZA4MjzIiazd1BYwA07/g5ALL77md8TEcC2jkNCZxDifGIWT80v/UW/bQ6fhZbx2lmV nKwBMfWClWjLw== Date: Tue, 30 Nov 2021 13:05:11 +0100 From: Frederic Weisbecker To: Nicolas Saenz Julienne Cc: linux-kernel , linux-arm-kernel , rcu@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Mark Rutland , Steven Rostedt , paulmck@kernel.org, mtosatti Subject: Re: Question WRT early IRQ/NMI entry code Message-ID: <20211130120511.GB599355@lothringen> References: <8719ad46cc29a2c5d7baac3c35770e5460ab8d5c.camel@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <8719ad46cc29a2c5d7baac3c35770e5460ab8d5c.camel@redhat.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211130_040519_907783_5A997298 X-CRM114-Status: GOOD ( 16.20 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org T24gVHVlLCBOb3YgMzAsIDIwMjEgYXQgMTI6Mjg6NDFQTSArMDEwMCwgTmljb2xhcyBTYWVueiBK dWxpZW5uZSB3cm90ZToKPiBIaSBBbGwsCj4gd2hpbGUgZ29pbmcgb3ZlciB0aGUgSVJRL05NSSBl bnRyeSBjb2RlIEkndmUgZm91bmQgYSBzbWFsbCAnaW5jb25zaXN0ZW5jeSc6Cj4gd2hpbGUgaW4g dGhlIElSUSBlbnRyeSBwYXRoLCB3ZSBpbmZvcm0gUkNVIG9mIHRoZSBjb250ZXh0IGNoYW5nZSAq YmVmb3JlKgo+IGluY3JlbWVudGluZyB0aGUgcHJlZW1wdCBjb3VudGVyLCB0aGUgb3Bwb3NpdGUg aGFwcGVucyBmb3IgdGhlIE5NSSBlbnRyeQo+IHBhdGguIFRoaXMgYXBwbGllcyB0byBib3RoIGFy bTY0IGFuZCB4ODZbMV0uCj4gCj4gQWN0dWFsbHksIHJjdV9ubWlfZW50ZXIoKSDigJQgd2hpY2gg aXMgYWxzbyB0aGUgbWFpbiBSQ1UgY29udGV4dCBzd2l0Y2ggZnVuY3Rpb24KPiBmb3IgdGhlIElS USBlbnRyeSBwYXRoIOKAlCB1c2VzIHRoZSBwcmVlbXB0IGNvdW50ZXIgdG8gdmVyaWZ5IGl0J3Mg bm90IGluIE5NSQo+IGNvbnRleHQuIFNvIGl0IHdvdWxkIG1ha2Ugc2Vuc2UgdG8gYXNzdW1lIGFs bCBjYWxsZXJzIGhhdmUgdGhlIHNhbWUgdXBkYXRlZAo+IHZpZXcgb2YgdGhlIHByZWVtcHQgY291 bnQsIHdoaWNoIGlzbid0IHRydWUgQVRNLgo+IAo+IEknbSBzdXJlIHRoZXJlIGFuIG9ic2N1cmUv bm9uLW9idmlvdXMgcmVhc29uIGZvciB0aGlzLCByaWdodD8KCkF0IGxlYXN0IEkgY2FuJ3QgZmlu ZCBhbiBpbW1lZGlhdGUgcmVhc29uIGZvciBpdCBlaXRoZXIgOi0pCgpUaGFua3MhCgpfX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpsaW51eC1hcm0ta2VybmVs IG1haWxpbmcgbGlzdApsaW51eC1hcm0ta2VybmVsQGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0cDov L2xpc3RzLmluZnJhZGVhZC5vcmcvbWFpbG1hbi9saXN0aW5mby9saW51eC1hcm0ta2VybmVsCg==