From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by sourceware.org (Postfix) with ESMTPS id 4BA23386EC7D for ; Wed, 9 Sep 2020 05:28:47 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 4BA23386EC7D Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 869E121D40; Wed, 9 Sep 2020 05:28:42 +0000 (UTC) Date: Wed, 9 Sep 2020 14:28:40 +0900 From: Masami Hiramatsu To: Masami Hiramatsu Cc: peterz@infradead.org, Ingo Molnar , linux-kernel@vger.kernel.org, Eddy_Wu@trendmicro.com, x86@kernel.org, davem@davemloft.net, rostedt@goodmis.org, naveen.n.rao@linux.ibm.com, anil.s.keshavamurthy@intel.com, linux-arch@vger.kernel.org, cameron@moodycamel.com, oleg@redhat.com, will@kernel.org, paulmck@kernel.org, systemtap@sourceware.org Subject: Re: [PATCH v5 00/21] kprobes: Unify kretprobe trampoline handlers and make kretprobe lockless Message-Id: <20200909142840.b2245ae2f8325f042a3bc546@kernel.org> In-Reply-To: <20200909000923.54cca4fb530904c57e8ff529@kernel.org> References: <159870598914.1229682.15230803449082078353.stgit@devnote2> <20200901190808.GK29142@worktop.programming.kicks-ass.net> <20200902093739.8bd13603380951eaddbcd8a5@kernel.org> <20200902070226.GG2674@hirez.programming.kicks-ass.net> <20200902171755.b126672093a3c5d1b3a62a4f@kernel.org> <20200902093613.GY1362448@hirez.programming.kicks-ass.net> <20200902221926.f5cae5b4ad00b8d8f9ad99c7@kernel.org> <20200902134252.GH1362448@hirez.programming.kicks-ass.net> <20200903103954.68f0c97da57b3679169ce3a7@kernel.org> <20200908103736.GP1362448@hirez.programming.kicks-ass.net> <20200909000923.54cca4fb530904c57e8ff529@kernel.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, RCVD_IN_BARRACUDACENTRAL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: systemtap@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Systemtap mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 Sep 2020 05:28:48 -0000 On Wed, 9 Sep 2020 00:09:23 +0900 Masami Hiramatsu wrote: > > > Of course make it lockless then warning is gone. > > > But even without the lockless patch, this warning can be false-positive > > > because we prohibit nested kprobe call, right? > > > > Yes, because the actual nesting is avoided by kprobe_busy, but lockdep > > can't tell. Lockdep sees a regular lock user and an in-nmi lock user and > > figures that's a bad combination. Hmm, what about introducing new LOCK_USED_KPROBE bit, which will be set if the lock is accessed when the current_kprobe is set (including kprobe_busy)? This means it is in the kprobe user-handler context. If we access the lock always in the kprobes context, it is never nested. Thank you, -- Masami Hiramatsu