51 lines
1.6 KiB
Diff
51 lines
1.6 KiB
Diff
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Wed, 25 May 2016 14:03:50 +0200
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Subject: [PATCH] trace: correct off by one while recording the trace-event
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz
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Trace events like raw_syscalls show always a preempt code of one. The
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reason is that on PREEMPT kernels rcu_read_lock_sched_notrace()
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increases the preemption counter and the function recording the counter
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is caller within the RCU section.
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Cc: stable-rt@vger.kernel.org
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/linux/tracepoint.h | 13 +++++++++++++
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kernel/trace/trace_events.c | 2 +-
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2 files changed, 14 insertions(+), 1 deletion(-)
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--- a/include/linux/tracepoint.h
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+++ b/include/linux/tracepoint.h
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@@ -33,6 +33,19 @@ struct trace_enum_map {
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#define TRACEPOINT_DEFAULT_PRIO 10
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+/*
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+ * The preempt count recorded in trace_event_raw_event_# are off by one due to
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+ * rcu_read_lock_sched_notrace() in __DO_TRACE. This is corrected here.
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+ */
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+static inline int event_preempt_count(void)
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+{
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+#ifdef CONFIG_PREEMPT
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+ return preempt_count() - 1;
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+#else
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+ return 0;
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+#endif
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+}
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+
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extern int
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tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data);
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extern int
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--- a/kernel/trace/trace_events.c
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+++ b/kernel/trace/trace_events.c
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@@ -243,7 +243,7 @@ void *trace_event_buffer_reserve(struct
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return NULL;
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local_save_flags(fbuffer->flags);
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- fbuffer->pc = preempt_count();
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+ fbuffer->pc = event_preempt_count();
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fbuffer->trace_file = trace_file;
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fbuffer->event =
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