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[71.56.235.36]) by smtp.gmail.com with ESMTPSA id p143sm1665093oop.14.2020.07.31.12.33.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Jul 2020 12:33:47 -0700 (PDT) Date: Fri, 31 Jul 2020 13:33:45 -0600 From: dann frazier To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Ian May Subject: Re: [for-next][PATCH 09/18] tracing: Move pipe reference to trace array instead of current_tracer Message-ID: <20200731193345.GA54749@xps13.dannf> References: <20200702215812.428188663@goodmis.org> <20200702215832.784471709@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200702215832.784471709@goodmis.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 02, 2020 at 05:58:21PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" > > 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. Thanks Steven! In case it helps backport consideration, I wanted to note that 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. -dann > Fixes: cf6ab6d9143b1 ("tracing: Add ref count to tracer for when they are being read by pipe") > Signed-off-by: Steven Rostedt (VMware) > --- > 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 8241d1448d70..64c5b8146cca 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -5891,7 +5891,7 @@ 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; > } > @@ -6107,7 +6107,7 @@ 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; > @@ -6126,7 +6126,7 @@ 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); > @@ -7428,7 +7428,7 @@ 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); > > @@ -7529,7 +7529,7 @@ 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); > > @@ -8737,7 +8737,7 @@ static int __remove_instance(struct trace_array *tr) > int i; > > /* Reference counter for a newly created trace array = 1. */ > - if (tr->ref > 1 || (tr->current_trace && tr->current_trace->ref)) > + if (tr->ref > 1 || (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 13db4000af3f..f21607f87189 100644 > --- a/kernel/trace/trace.h > +++ b/kernel/trace/trace.h > @@ -356,6 +356,7 @@ 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; > @@ -547,7 +548,6 @@ struct tracer { > struct tracer *next; > struct tracer_flags *flags; > int enabled; > - int ref; > bool print_max; > bool allow_instances; > #ifdef CONFIG_TRACER_MAX_TRACE