From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions Date: Mon, 24 Feb 2020 11:10:50 +0100 Message-ID: <20200224101050.GE14897@hirez.programming.kicks-ass.net> References: <20200221133416.777099322@infradead.org> <20200221134215.090538203@infradead.org> <20200222030843.GA191380@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from bombadil.infradead.org ([198.137.202.133]:41050 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726452AbgBXKLW (ORCPT ); Mon, 24 Feb 2020 05:11:22 -0500 Content-Disposition: inline In-Reply-To: <20200222030843.GA191380@google.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org On Fri, Feb 21, 2020 at 10:08:43PM -0500, Joel Fernandes wrote: > On Fri, Feb 21, 2020 at 02:34:17PM +0100, Peter Zijlstra wrote: > > nmi_enter() does lockdep_off() and hence lockdep ignores everything. > > > > And NMI context makes it impossible to do full IN-NMI tracking like we > > do IN-HARDIRQ, that could result in graph_lock recursion. > > The patch makes sense to me. > > Reviewed-by: Joel Fernandes (Google) > > NOTE: > Also, I was wondering if we can detect the graph_lock recursion case and > avoid doing anything bad, that way we enable more of the lockdep > functionality for NMI where possible. Not sure if the suggestion makes sense > though! Yeah, I considered playing trylock games, but figured I shouldn't make it more complicated that it needs to be.