DEBUG percpu-recount: Crude printk dumps

It should not be too noisy since only cgroups use the confirm_kill callback hence percpu_ref_call_confirm_rcu() should only run once per css. Signed-off-by: Michal Koutný <mkoutny@suse.com>
Werkov · May 26, 2022 · ebd2282 · ebd2282
1 parent ef13021
commit ebd2282
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Showing 3 changed files with 8 additions and 2 deletions.
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
@@ -5552,7 +5552,9 @@ static void css_killed_work_fn(struct work_struct *work)
 
 	do {
 		offline_css(css);
+		trace_printk("%p pre-put %lu\n", css, atomic_long_read(&css->refcnt.data->count));
 		css_put(css);
+		trace_printk("%p post-put %lu\n", css, atomic_long_read(&css->refcnt.data->count));
 		/* @css can't go away while we're holding cgroup_mutex */
 		css = css->parent;
 	} while (css && atomic_dec_and_test(&css->online_cnt));

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
@@ -134,7 +134,7 @@ cpumask_var_t __read_mostly	tracing_buffer_mask;
  * Set 2 if you want to dump the buffer of the CPU that triggered oops
  */
 
-enum ftrace_dump_mode ftrace_dump_on_oops;
+enum ftrace_dump_mode ftrace_dump_on_oops = DUMP_ALL;
 
 /* When set, tracing will stop when a WARN*() is hit */
 int __disable_trace_on_warning;

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
@@ -152,15 +152,19 @@ static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
 			struct percpu_ref_data, rcu);
 	struct percpu_ref *ref = data->ref;
 
+	trace_printk("pre-conf %lu\n", atomic_long_read(&data->count));
 	data->confirm_switch(ref);
 	data->confirm_switch = NULL;
+	trace_printk("post-conf %lu\n", atomic_long_read(&data->count));
 	wake_up_all(&percpu_ref_switch_waitq);
 
 	if (!data->allow_reinit)
 		__percpu_ref_exit(ref);
 
+	trace_printk("pre-put %lu\n", atomic_long_read(&data->count));
 	/* drop ref from percpu_ref_switch_to_atomic() */
 	percpu_ref_put(ref);
+	trace_printk("post-put %lu\n", atomic_long_read(&data->count));
 }
 
 static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
@@ -176,7 +180,7 @@ static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
 	for_each_possible_cpu(cpu)
 		count += *per_cpu_ptr(percpu_count, cpu);
 
-	pr_debug("global %lu percpu %lu\n",
+	trace_printk("global %lu percpu %lu\n",
 		 atomic_long_read(&data->count), count);
 
 	/*