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Date: Thu, 23 Sep 2021 11:42:56 +0800 From: 王贇 <yun.wang@...ux.alibaba.com> To: Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com>, open list <linux-kernel@...r.kernel.org> Subject: [RFC PATCH] trace: prevent preemption in perf_ftrace_function_call() 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; 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) -- 1.8.3.1
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