From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1F81EC4332F for ; Tue, 1 Nov 2022 22:44:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231258AbiKAWoH (ORCPT ); Tue, 1 Nov 2022 18:44:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48904 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230440AbiKAWnw (ORCPT ); Tue, 1 Nov 2022 18:43:52 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9ED401DF29 for ; Tue, 1 Nov 2022 15:43:51 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 5C144B81DA0 for ; Tue, 1 Nov 2022 22:43:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF5D9C433C1; Tue, 1 Nov 2022 22:43:48 +0000 (UTC) Date: Tue, 1 Nov 2022 18:43:47 -0400 From: Steven Rostedt To: Roland Ruckerbauer Cc: Masami Hiramatsu , linux-kernel@vger.kernel.org, Takashi Iwai , regressions@lists.linux.dev, Steven Noonan Subject: Re: [BUG] NULL pointer dereference probably caused by kernel/trace/ring_buffer.c Message-ID: <20221101184347.2ecce20c@rorschach.local.home> In-Reply-To: <20221101183512.285cfd68@rorschach.local.home> References: <20221031145046.2a7f9d32@rorschach.local.home> <20221101153135.5345c748@rorschach.local.home> <20221101173802.7a476a04@rorschach.local.home> <20221101183512.285cfd68@rorschach.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 1 Nov 2022 18:35:12 -0400 Steven Rostedt wrote: > OK, this is a great clue. I'll dig deeper. One more NULL check. And this one is legit, and I'm betting is the fix. The buffer->buffers is allocated to nr_cpu_ids, but are only initialized for online CPUs. If you have a CPU that is not yet initialized (or may never be), then the cpu_buffer will be NULL. -- Steve diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 199759c73519..4ffcc6e33258 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -937,6 +937,9 @@ void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu) struct ring_buffer_per_cpu *cpu_buffer; struct rb_irq_work *rbwork; + if (!buffer) + return; + if (cpu == RING_BUFFER_ALL_CPUS) { /* Wake up individual ones too. One level recursion */ @@ -945,7 +948,14 @@ void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu) rbwork = &buffer->irq_work; } else { + if (WARN_ON_ONCE(!buffer->buffers)) + return; + if (WARN_ON_ONCE(cpu >= nr_cpu_ids)) + return; cpu_buffer = buffer->buffers[cpu]; + /* The CPU buffer may not have been initialized yet */ + if (!cpu_buffer) + return; rbwork = &cpu_buffer->irq_work; }