From patchwork Wed Aug 12 20:53:22 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: dann frazier X-Patchwork-Id: 266580 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7BD48C433E0 for ; Wed, 12 Aug 2020 20:53:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5FC552076C for ; Wed, 12 Aug 2020 20:53:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726030AbgHLUx2 (ORCPT ); Wed, 12 Aug 2020 16:53:28 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:38018 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726526AbgHLUx2 (ORCPT ); Wed, 12 Aug 2020 16:53:28 -0400 Received: from 2.general.dannf.us.vpn ([10.172.65.1] helo=localhost) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1k5xkT-0007fx-ND; Wed, 12 Aug 2020 20:53:26 +0000 From: dann frazier To: stable@vger.kernel.org, "Steven Rostedt (VMware)" Subject: [PATCH 5.4] tracing: Move pipe reference to trace array instead of current_tracer Date: Wed, 12 Aug 2020 14:53:22 -0600 Message-Id: <20200812205322.229101-1-dann.frazier@canonical.com> X-Mailer: git-send-email 2.28.0 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: "Steven Rostedt (VMware)" commit 7ef282e05132d56b6f6b71e3873f317664bea78b upstream If a process has the trace_pipe open on a trace_array, the current tracer for that trace array should not be changed. This was original enforced by a global lock, but when instances were introduced, it was moved to the current_trace. But this structure is shared by all instances, and a trace_pipe is for a single instance. There's no reason that a process that has trace_pipe open on one instance should prevent another instance from changing its current tracer. Move the reference counter to the trace_array instead. This is marked as "Fixes" but is more of a clean up than a true fix. Backport if you want, but its not critical. Fixes: cf6ab6d9143b1 ("tracing: Add ref count to tracer for when they are being read by pipe") Signed-off-by: Steven Rostedt (VMware) Cc: stable@vger.kernel.org # 5.4.x [Resolved conflict in __remove_instance()] Signed-off-by: dann frazier --- This addresses an issue we've seen with users trying to change current_tracer when they happen to have rasdaemon installed. rasdaemon uses the trace_pipe interface at runtime, which therefore blocks changing the current tracer. But of course, unless you know about rasdaemon internals, it isn't exactly an obvious failure mode. Conflict in __remove_instance() was due to a change in reference counter semantics introduced later in v5.5 via commit 288797871473 "tracing: Adding new functions for kernel access to Ftrace instances". Resolved by leaving the first test in the if statement as it was in v5.4. kernel/trace/trace.c | 12 ++++++------ kernel/trace/trace.h | 2 +- 2 files changed, 7 insertions(+), 7 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 721947b9962d..f9c2bdbbd893 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5686,7 +5686,7 @@ static int tracing_set_tracer(struct trace_array *tr, const char *buf) } /* If trace pipe files are being read, we can't change the tracer */ - if (tr->current_trace->ref) { + if (tr->trace_ref) { ret = -EBUSY; goto out; } @@ -5902,7 +5902,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp) nonseekable_open(inode, filp); - tr->current_trace->ref++; + tr->trace_ref++; out: mutex_unlock(&trace_types_lock); return ret; @@ -5921,7 +5921,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file) mutex_lock(&trace_types_lock); - tr->current_trace->ref--; + tr->trace_ref--; if (iter->trace->pipe_close) iter->trace->pipe_close(iter); @@ -7230,7 +7230,7 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp) filp->private_data = info; - tr->current_trace->ref++; + tr->trace_ref++; mutex_unlock(&trace_types_lock); @@ -7331,7 +7331,7 @@ static int tracing_buffers_release(struct inode *inode, struct file *file) mutex_lock(&trace_types_lock); - iter->tr->current_trace->ref--; + iter->tr->trace_ref--; __trace_array_put(iter->tr); @@ -8470,7 +8470,7 @@ static int __remove_instance(struct trace_array *tr) { int i; - if (tr->ref || (tr->current_trace && tr->current_trace->ref)) + if (tr->ref || (tr->current_trace && tr->trace_ref)) return -EBUSY; list_del(&tr->list); diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index a3c29d5fcc61..4055158c1dd2 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -309,6 +309,7 @@ struct trace_array { struct trace_event_file *trace_marker_file; cpumask_var_t tracing_cpumask; /* only trace on set CPUs */ int ref; + int trace_ref; #ifdef CONFIG_FUNCTION_TRACER struct ftrace_ops *ops; struct trace_pid_list __rcu *function_pids; @@ -498,7 +499,6 @@ struct tracer { struct tracer *next; struct tracer_flags *flags; int enabled; - int ref; bool print_max; bool allow_instances; #ifdef CONFIG_TRACER_MAX_TRACE