From 561a4fe851ccab9dd0d14989ab566f9392d9f8b5 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" Date: Fri, 2 May 2014 13:30:04 -0400 Subject: [PATCH] tracing: Use rcu_dereference_sched() for trace event triggers As trace event triggers are now part of the mainline kernel, I added my trace event trigger tests to my test suite I run on all my kernels. Now these tests get run under different config options, and one of those options is CONFIG_PROVE_RCU, which checks under lockdep that the rcu locking primitives are being used correctly. This triggered the following splat: =============================== [ INFO: suspicious RCU usage. ] 3.15.0-rc2-test+ #11 Not tainted ------------------------------- kernel/trace/trace_events_trigger.c:80 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 0 4 locks held by swapper/1/0: #0: ((&(&j_cdbs->work)->timer)){..-...}, at: [] call_timer_fn+0x5/0x1be #1: (&(&pool->lock)->rlock){-.-...}, at: [] __queue_work+0x140/0x283 #2: (&p->pi_lock){-.-.-.}, at: [] try_to_wake_up+0x2e/0x1e8 #3: (&rq->lock){-.-.-.}, at: [] try_to_wake_up+0x1a0/0x1e8 stack backtrace: CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.15.0-rc2-test+ #11 Hardware name: /DG965MQ, BIOS MQ96510J.86A.0372.2006.0605.1717 06/05/2006 0000000000000001 ffff88007e083b98 ffffffff819f53a5 0000000000000006 ffff88007b0942c0 ffff88007e083bc8 ffffffff81081307 ffff88007ad96d20 0000000000000000 ffff88007af2d840 ffff88007b2e701c ffff88007e083c18 Call Trace: [] dump_stack+0x4f/0x7c [] lockdep_rcu_suspicious+0x107/0x110 [] event_triggers_call+0x99/0x108 [] ftrace_event_buffer_commit+0x42/0xa4 [] ftrace_raw_event_sched_wakeup_template+0x71/0x7c [] ttwu_do_wakeup+0x7f/0xff [] ttwu_do_activate.constprop.126+0x5c/0x61 [] try_to_wake_up+0x1ac/0x1e8 [] wake_up_process+0x36/0x3b [] wake_up_worker+0x24/0x26 [] insert_work+0x5c/0x65 [] __queue_work+0x26c/0x283 [] ? __queue_work+0x283/0x283 [] delayed_work_timer_fn+0x1e/0x20 [] call_timer_fn+0xdf/0x1be^M [] ? call_timer_fn+0x5/0x1be [] ? __queue_work+0x283/0x283 [] run_timer_softirq+0x1a4/0x22f^M [] __do_softirq+0x17b/0x31b^M [] irq_exit+0x42/0x97 [] smp_apic_timer_interrupt+0x37/0x44 [] apic_timer_interrupt+0x6f/0x80 [] ? default_idle+0x21/0x32 [] ? default_idle+0x1f/0x32 [] arch_cpu_idle+0xf/0x11 [] cpu_startup_entry+0x1a3/0x213 [] start_secondary+0x212/0x219 The cause is that the triggers are protected by rcu_read_lock_sched() but the data is dereferenced with rcu_dereference() which expects it to be protected with rcu_read_lock(). The proper reference should be rcu_dereference_sched(). Cc: Tom Zanussi Cc: stable@vger.kernel.org # 3.14+ Signed-off-by: Steven Rostedt --- kernel/trace/trace_events_trigger.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c index 925f537f07d1..4747b476a030 100644 --- a/kernel/trace/trace_events_trigger.c +++ b/kernel/trace/trace_events_trigger.c @@ -77,7 +77,7 @@ event_triggers_call(struct ftrace_event_file *file, void *rec) data->ops->func(data); continue; } - filter = rcu_dereference(data->filter); + filter = rcu_dereference_sched(data->filter); if (filter && !filter_match_preds(filter, rec)) continue; if (data->cmd_ops->post_trigger) { -- 2.20.1