Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934316AbeAIQOO (ORCPT + 1 other); Tue, 9 Jan 2018 11:14:14 -0500 Received: from bombadil.infradead.org ([65.50.211.133]:54707 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933255AbeAIQOK (ORCPT ); Tue, 9 Jan 2018 11:14:10 -0500 Date: Tue, 9 Jan 2018 17:14:00 +0100 From: Peter Zijlstra To: Vince Weaver Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Ingo Molnar , Arnaldo Carvalho de Melo , Thomas Gleixner , Steven Rostedt Subject: Re: perf: perf_fuzzer quickly locks up on 4.15-rc7 Message-ID: <20180109161400.GC2369@hirez.programming.kicks-ass.net> References: <20180108173005.lkglqrixb2ota6g2@gmail.com> <20180109102507.GG6176@hirez.programming.kicks-ass.net> <20180109132602.GA2369@hirez.programming.kicks-ass.net> <20180109151253.GK6176@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180109151253.GK6176@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Tue, Jan 09, 2018 at 04:12:53PM +0100, Peter Zijlstra wrote: > In any case, I found yet another lockdep splat, trying to figure out wth > to do about that. An of course, testing this one yields yet another lockdep splat.. onwards to #3 :/ --- Subject: perf: Fix another perf,trace,cpuhp lock inversion From: Peter Zijlstra Date: Tue Jan 9 17:07:59 CET 2018 Lockdep complained about: perf_trace_init() #0 mutex_lock(&event_mutex) perf_trace_event_init() perf_trace_event_reg() tp_event->class->reg() := tracepoint_probe_register #1 mutex_lock(&tracepoints_mutex) trace_point_add_func() #2 static_key_enable() #2 do_cpu_up() perf_event_init_cpu() #3 mutex_lock(&pmus_lock) #4 mutex_lock(&ctx->mutex) perf_ioctl() #4 ctx = perf_event_ctx_lock() _perf_iotcl() ftrace_profile_set_filter() #0 mutex_lock(&event_mutex) Fudge it for now by noting that the tracepoint state does not depend on the event <-> context relation. Ugly though :/ Cc: Thomas Gleixner Cc: Steven Rostedt Signed-off-by: Peter Zijlstra (Intel) --- kernel/events/core.c | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8525,6 +8525,29 @@ perf_event_set_addr_filter(struct perf_e return ret; } +static int +perf_tracepoint_set_filter(struct perf_event *event, char *filter_str) +{ + struct perf_event_context *ctx = event->ctx; + int ret; + + /* + * Beware, here be dragons!! + * + * the tracepoint muck will deadlock against ctx->mutex, but the tracepoint + * stuff does not actually need it. So temporarily drop ctx->mutex. As per + * perf_event_ctx_lock() we already have a reference on ctx. + * + * This can result in event getting moved to a different ctx, but that + * does not affect the tracepoint state. + */ + mutex_unlock(&ctx->mutex); + ret = ftrace_profile_set_filter(event, event->attr.config, filter_str); + mutex_lock(&ctx->mutex); + + return ret; +} + static int perf_event_set_filter(struct perf_event *event, void __user *arg) { char *filter_str; @@ -8541,8 +8564,7 @@ static int perf_event_set_filter(struct if (IS_ENABLED(CONFIG_EVENT_TRACING) && event->attr.type == PERF_TYPE_TRACEPOINT) - ret = ftrace_profile_set_filter(event, event->attr.config, - filter_str); + ret = perf_tracepoint_set_filter(event, filter_str); else if (has_addr_filter(event)) ret = perf_event_set_addr_filter(event, filter_str);