Messages in this thread | | | Date | Fri, 3 Aug 2018 16:32:09 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] trace: Use rcu_dereference_raw for hooks from trace-event subsystem |
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On Thu, 2 Aug 2018 19:34:07 -0700 "Joel Fernandes (Google)" <joel@joelfernandes.org> wrote:
> Since we switched to using SRCU for tracepoints used in the idle path, > we can no longer use rcu_dereference_sched for dereferencing points in > trace-event hooks. > > Since tracepoints can now use either SRCU or sched-RCU, just use > rcu_dereference_raw for traceevents just like we're doing when > dereferencing the tracepoint table.
OK, I've tested that this fixes the bug.
/mnt/ftrace # ./ftracetest test.d/event/toplevel-enable.tc === Ftrace unit tests === [1] event tracing - enable/disable with top level files [PASS]
# of passed: 1 # of failed: 0 # of unresolved: 0 # of untested: 0 # of unsupported: 0 # of xfailed: 0 # of undefined(test bug): 0
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Thank you!
> > This prevents an RCU warning reported by Masami: > > [ 282.060593] WARNING: can't dereference registers at 00000000f3c7f62b > [ 282.063200] ============================= > [ 282.064082] WARNING: suspicious RCU usage > [ 282.064963] 4.18.0-rc6+ #15 Tainted: G W > [ 282.066048] ----------------------------- > [ 282.066923] /home/mhiramat/ksrc/linux/kernel/trace/trace_events.c:242 > suspicious rcu_dereference_check() usage! > [ 282.068974] > [ 282.068974] other info that might help us debug this: > [ 282.068974] > [ 282.070770] > [ 282.070770] RCU used illegally from idle CPU! > [ 282.070770] rcu_scheduler_active = 2, debug_locks = 1 > [ 282.072938] RCU used illegally from extended quiescent state! > [ 282.074183] no locks held by swapper/0/0. > [ 282.075071] > [ 282.075071] stack backtrace: > [ 282.076121] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W > [ 282.077782] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) > [ 282.079604] Call Trace: > [ 282.080212] <IRQ> > [ 282.080755] dump_stack+0x85/0xcb > [ 282.081523] trace_event_ignore_this_pid+0x66/0x70 > [ 282.082541] trace_event_raw_event_preemptirq_template+0xa2/0xb0 > [ 282.083774] ? interrupt_entry+0xc4/0xe0 > [ 282.084665] ? trace_hardirqs_off_thunk+0x1a/0x1c > [ 282.085669] trace_hardirqs_off_caller+0x90/0xd0 > [ 282.086597] trace_hardirqs_off_thunk+0x1a/0x1c > [ 282.087433] ? call_function_interrupt+0xa/0x20 > [ 282.088201] interrupt_entry+0xc4/0xe0 > [ 282.088848] ? call_function_interrupt+0xa/0x20 > [ 282.089579] </IRQ> > [ 282.090029] ? native_safe_halt+0x2/0x10 > [ 282.090695] ? default_idle+0x1f/0x160 > [ 282.091330] ? default_idle_call+0x24/0x40 > [ 282.091997] ? do_idle+0x210/0x250 > [ 282.092658] ? cpu_startup_entry+0x6f/0x80 > [ 282.093338] ? start_kernel+0x49d/0x4bd > [ 282.093987] ? secondary_startup_64+0xa5/0xb0 > > Reported-by: Masami Hiramatsu <mhiramat@kernel.org> > Fixes: e6753f23d961 ("tracepoint: Make rcuidle tracepoint callers use SRCU") > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> > --- > kernel/trace/trace_events.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index 14ff4ff3caab..7b508ce8ac44 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -239,7 +239,7 @@ bool trace_event_ignore_this_pid(struct trace_event_file *trace_file) > struct trace_array_cpu *data; > struct trace_pid_list *pid_list; > > - pid_list = rcu_dereference_sched(tr->filtered_pids); > + pid_list = rcu_dereference_raw(tr->filtered_pids); > if (!pid_list) > return false; > > @@ -512,7 +512,7 @@ event_filter_pid_sched_process_exit(void *data, struct task_struct *task) > struct trace_pid_list *pid_list; > struct trace_array *tr = data; > > - pid_list = rcu_dereference_sched(tr->filtered_pids); > + pid_list = rcu_dereference_raw(tr->filtered_pids); > trace_filter_add_remove_task(pid_list, NULL, task); > } > > -- > 2.18.0.597.ga71716f1ad-goog >
-- Masami Hiramatsu <mhiramat@kernel.org>
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