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[209.85.218.45]) by smtp.gmail.com with ESMTPSA id r8sm10036556edy.87.2020.09.14.14.06.46 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Sep 2020 14:06:46 -0700 (PDT) Received: by mail-ej1-f45.google.com with SMTP id r7so1909528ejs.11 for ; Mon, 14 Sep 2020 14:06:46 -0700 (PDT) X-Received: by 2002:a2e:91cd:: with SMTP id u13mr5091065ljg.421.1600117171599; Mon, 14 Sep 2020 13:59:31 -0700 (PDT) MIME-Version: 1.0 References: <20200914204209.256266093@linutronix.de> In-Reply-To: <20200914204209.256266093@linutronix.de> From: Linus Torvalds Date: Mon, 14 Sep 2020 13:59:15 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 00/13] preempt: Make preempt count unconditional To: Thomas Gleixner Cc: LKML , linux-arch , Sebastian Andrzej Siewior , Valentin Schneider , Richard Henderson , Ivan Kokshaysky , Matt Turner , alpha , Jeff Dike , Richard Weinberger , Anton Ivanov , linux-um , Brian Cain , linux-hexagon@vger.kernel.org, Geert Uytterhoeven , linux-m68k , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Will Deacon , Andrew Morton , Linux-MM , Ingo Molnar , Russell King , Linux ARM , Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , intel-gfx , dri-devel , "Paul E. McKenney" , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , Shuah Khan , rcu@vger.kernel.org, "open list:KERNEL SELFTEST FRAMEWORK" Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 2936A180AD804 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Sep 14, 2020 at 1:45 PM Thomas Gleixner wrote: > > Recently merged code does: > > gfp = preemptible() ? GFP_KERNEL : GFP_ATOMIC; > > Looks obviously correct, except for the fact that preemptible() is > unconditionally false for CONFIF_PREEMPT_COUNT=n, i.e. all allocations in > that code use GFP_ATOMIC on such kernels. I don't think this is a good reason to entirely get rid of the no-preempt thing. The above is just garbage. It's bogus. You can't do it. Blaming the no-preempt code for this bug is extremely unfair, imho. And the no-preempt code does help make for much better code generation for simple spinlocks. Where is that horribly buggy recent code? It's not in that exact format, certainly, since 'grep' doesn't find it. Linus