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[86.9.19.6]) by smtp.gmail.com with ESMTPSA id d191sm2301565wmd.44.2020.06.03.05.00.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Jun 2020 05:00:53 -0700 (PDT) Date: Wed, 3 Jun 2020 13:00:51 +0100 From: Daniel Thompson To: Doug Anderson Cc: Jason Wessel , Sumit Garg , kgdb-bugreport@lists.sourceforge.net, LKML Subject: Re: [PATCH] kgdb: Avoid suspicious RCU usage warning Message-ID: <20200603120051.dxpavvsxvsxnvuct@holly.lan> References: <20200507153444.1.I70e0d4fd46d5ed2aaf0c98a355e8e1b7a5bb7e4e@changeid> <20200519104151.6evv3hizm5dbjjq2@holly.lan> <20200601161952.3hx6sv5hzdnjnvtj@holly.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 02, 2020 at 03:56:33PM -0700, Doug Anderson wrote: > > > 2. Perhaps remove the whole irq saving / restoring in kgdb_cpu_enter(). > > > > Are you feeling lucky? > > > > I think there will come a time when bravery is called for but I'd rather > > see this as part of a bigger rewrite instead of a single high risk > > change. > > Hrm, maybe. I guess it depends on whether we want to take baby steps > there or try to do it all at once. If we take baby steps we will > occasionally fall down but we'll slowly start getting things cleaned > up. If we wait for a full rewrite then we might be waiting for a long > time. It'll also be harder to figure out which of the big changes in > the major rewrite broken someone. ...or if the major rewrite comes in > 20 small/bisectable patches it may be hard to revert patch 2 out of 20 > if the future patches all build upon it. If we do one small high-risk > change and then wait before building upon it then it'll be easy for > someone to bisect and then yell for a revert. My views are a bit too nuanced for me to agree or disagree with this. I'm not against baby steps and I definitely *don't* want kgdb to continue to be preserved in aspic. However I'm still reluctant to start our baby steps with a "let's see if this breaks something" patch given we know it could be a very large number of kernel cycles before we get an answer. I would be much happier if those baby steps started, for example, with refactoring to decompose the beast into clearer (and dare I say better documented) functions. Or put another way, even if someone sent me 20 small bisectable patches in a single kernel cycle I'd still want the high risk bits to be towards the end of the patch set. Daniel.