From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
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@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 5.4.x
[Resolved conflict in __remove_instance()]
Signed-off-by: dann frazier <dann.frazier@xxxxxxxxxxxxx>
---
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
--
2.28.0
