tracing: Fix using ret variable in tracing_set_tracer()

JIRA: https://issues.redhat.com/browse/RHEL-86682

commit 22bec11
Author: Steven Rostedt <rostedt@goodmis.org>
Date:   Mon Jan 6 11:11:43 2025 -0500

    tracing: Fix using ret variable in tracing_set_tracer()

    When the function tracing_set_tracer() switched over to using the guard()
    infrastructure, it did not need to save the 'ret' variable and would just
    return the value when an error arised, instead of setting ret and jumping
    to an out label.

    When CONFIG_TRACER_SNAPSHOT is enabled, it had code that expected the
    "ret" variable to be initialized to zero and had set 'ret' while holding
    an arch_spin_lock() (not used by guard), and then upon releasing the lock
    it would check 'ret' and exit if set. But because ret was only set when an
    error occurred while holding the locks, 'ret' would be used uninitialized
    if there was no error. The code in the CONFIG_TRACER_SNAPSHOT block should
    be self contain. Make sure 'ret' is also set when no error occurred.

    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Link: https://lore.kernel.org/20250106111143.2f90ff65@gandalf.local.home
    Reported-by: kernel test robot <lkp@intel.com>
    Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
    Closes: https://lore.kernel.org/r/202412271654.nJVBuwmF-lkp@intel.com/
    Fixes: d33b10c ("tracing: Switch trace.c code over to use guard()")
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
    Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Author: jeromemarchand

kernel/trace/trace.c

@@ -6134,8 +6134,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 	if (t->use_max_tr) {
 		local_irq_disable();
 		arch_spin_lock(&tr->max_lock);
-		if (tr->cond_snapshot)
-			ret = -EBUSY;
+		ret = tr->cond_snapshot ? -EBUSY : 0;
 		arch_spin_unlock(&tr->max_lock);
 		local_irq_enable();
 		if (ret)