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Date: Thu, 23 Sep 2021 09:33:59 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: 王贇 <yun.wang@...ux.alibaba.com> Cc: Ingo Molnar <mingo@...hat.com>, open list <linux-kernel@...r.kernel.org> Subject: Re: [RFC PATCH] trace: prevent preemption in perf_ftrace_function_call() On Thu, 23 Sep 2021 11:42:56 +0800 王贇 <yun.wang@...ux.alibaba.com> wrote: > With CONFIG_DEBUG_PREEMPT we observed reports like: > > BUG: using smp_processor_id() in preemptible > caller is perf_ftrace_function_call+0x6f/0x2e0 > CPU: 1 PID: 680 Comm: a.out Not tainted > Call Trace: > <TASK> > dump_stack_lvl+0x8d/0xcf > check_preemption_disabled+0x104/0x110 > ? optimize_nops.isra.7+0x230/0x230 > ? text_poke_bp_batch+0x9f/0x310 > perf_ftrace_function_call+0x6f/0x2e0 > ... > __text_poke+0x5/0x620 > text_poke_bp_batch+0x9f/0x310 > > This tell us the CPU could be changed after task is preempted, and > the checking on CPU before preemption is helpless. > > This patch just turn off preemption in perf_ftrace_function_call() > to prevent CPU changing. > > Signed-off-by: Michael Wang <yun.wang@...ux.alibaba.com> > --- > kernel/trace/trace_event_perf.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c > index 6aed10e..5486b18 100644 > --- a/kernel/trace/trace_event_perf.c > +++ b/kernel/trace/trace_event_perf.c > @@ -438,15 +438,17 @@ void perf_trace_buf_update(void *record, u16 type) > int rctx; > int bit; > > + preempt_disable_notrace(); > + > if (!rcu_is_watching()) > - return; > + goto out; You don't need preemption disabled for the above check. It's better to disable it here and leave the above return untouched. -- Steve > > if ((unsigned long)ops->private != smp_processor_id()) > - return; > + goto out; > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > - return; > + goto out; > > event = container_of(ops, struct perf_event, ftrace_ops); > > @@ -468,16 +470,18 @@ void perf_trace_buf_update(void *record, u16 type) > > entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx); > if (!entry) > - goto out; > + goto out_unlock; > > entry->ip = ip; > entry->parent_ip = parent_ip; > perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN, > 1, ®s, &head, NULL); > > -out: > +out_unlock: > ftrace_test_recursion_unlock(bit); > #undef ENTRY_SIZE > +out: > + preempt_enable_notrace(); > } > > static int perf_ftrace_function_register(struct perf_event *event)
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