From: "Steven Rostedt (VMware)" rostedt@goodmis.org

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) rostedt@goodmis.org Cc: stable@vger.kernel.org # 5.4.x [Resolved conflict in __remove_instance()] Signed-off-by: dann frazier dann.frazier@canonical.com --- 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