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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7DF70C4360F for ; Thu, 4 Apr 2019 13:29:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 48D76206B7 for ; Thu, 4 Apr 2019 13:29:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729886AbfDDN3v (ORCPT ); Thu, 4 Apr 2019 09:29:51 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:60357 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729128AbfDDN3s (ORCPT ); Thu, 4 Apr 2019 09:29:48 -0400 Received: by atrey.karlin.mff.cuni.cz (Postfix, from userid 512) id D679380402; Thu, 4 Apr 2019 15:29:38 +0200 (CEST) Date: Thu, 4 Apr 2019 15:22:02 +0200 From: Pavel Machek To: Steven Rostedt Cc: Doug Anderson , Sasha Levin , LKML , stable@vger.kernel.org Subject: Re: [PATCH AUTOSEL 5.0 011/262] tracing: kdb: Fix ftdump to not sleep Message-ID: <20190404132202.GC6124@xo-6d-61-c0.localdomain> References: <20190327180158.10245-1-sashal@kernel.org> <20190327180158.10245-11-sashal@kernel.org> <20190328101342.GD19456@atrey.karlin.mff.cuni.cz> <20190328161228.24f5aabd@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190328161228.24f5aabd@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2019-03-28 16:12:28, Steven Rostedt wrote: > On Thu, 28 Mar 2019 12:45:18 -0700 > Doug Anderson wrote: > > > > I see solution is simple, but now we have a loop with GFP_ATOMIC > > > allocations inside. How many "tracing spus" is this expected to loop > > > over? Will not it exhaust atomically available pages and reliably fail > > > in common configurations? > > > Pavel > > > > Each one of these allocations is ~32 bytes and you do one per CPU. > > Even with systems with a lot of CPUs that's not going to be tons. > > ...and you only do it with GFP_ATOMIC when you're actively dropped > > into kdb and debugging. It seems like going for simplicity is the > > right call here, but of course if Steven or Daniel say that it has to > > be done a different way then they're the true authorities. > > I really don't care. The code in question is only affected when we have > CONFIG_KGDB_KDB enabled. But as it gets called from an atomic context, > is it any different than what it was doing before? Except now with > GFP_ATOMIC it is actually safer. > > Now, we could add some helper functions in the ring-buffer code to > allow us to pre-allocate the ring_buffer_iter at boot up. Then we could > pass in the per-allocated iters and use them here. Ok, I guess 32 bytes is small enough, I somehow imagined it would be bigger... -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html