From: "Steven Rostedt (Red Hat)" Add the kernel command line tp_printk option that will have tracepoints that are active sent to printk() as well as to the trace buffer. Passing "tp_printk" will activate this. To turn it off, the sysctl /proc/sys/kernel/tracepoint_printk can have '0' echoed into it. Note, this only works if the cmdline option is used. Echoing 1 into the sysctl file without the cmdline option will have no affect. Note, this is a dangerous option. Having high frequency tracepoints send their data to printk() can possibly cause a live lock. This is another reason why this is only active if the command line option is used. Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1412121539300.16494@nanos Suggested-by: Thomas Gleixner Tested-by: Thomas Gleixner Acked-by: Thomas Gleixner Signed-off-by: Steven Rostedt --- Documentation/kernel-parameters.txt | 18 ++++++++++++++++++ include/linux/ftrace.h | 1 + kernel/sysctl.c | 7 +++++++ kernel/trace/trace.c | 17 +++++++++++++++++ kernel/trace/trace.h | 1 + kernel/trace/trace_events.c | 32 ++++++++++++++++++++++++++++++++ 6 files changed, 76 insertions(+) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 1d09eb37c562..ae41f1181e9a 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3500,6 +3500,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted. See also Documentation/trace/ftrace.txt "trace options" section. + tp_printk[FTRACE] + Have the tracepoints sent to printk as well as the + tracing ring buffer. This is useful for early boot up + where the system hangs or reboots and does not give the + option for reading the tracing buffer or performing a + ftrace_dump_on_oops. + + To turn off having tracepoints sent to printk, + echo 0 > /proc/sys/kernel/tracepoint_printk + Note, echoing 1 into this file without the + tracepoint_printk kernel cmdline option has no effect. + + ** CAUTION ** + + Having tracepoints sent to printk() and activating high + frequency tracepoints such as irq or sched, can cause + the system to live lock. + traceoff_on_warning [FTRACE] enable this option to disable tracing when a warning is hit. This turns off "tracing_on". Tracing can diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index f4bc14b7d444..1da602982cf9 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -879,6 +879,7 @@ static inline int test_tsk_trace_graph(struct task_struct *tsk) enum ftrace_dump_mode; extern enum ftrace_dump_mode ftrace_dump_on_oops; +extern int tracepoint_printk; extern void disable_trace_on_warning(void); extern int __disable_trace_on_warning; diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 4aada6d9fe74..bb50c2187194 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -622,6 +622,13 @@ static struct ctl_table kern_table[] = { .mode = 0644, .proc_handler = proc_dointvec, }, + { + .procname = "tracepoint_printk", + .data = &tracepoint_printk, + .maxlen = sizeof(tracepoint_printk), + .mode = 0644, + .proc_handler = proc_dointvec, + }, #endif #ifdef CONFIG_KEXEC { diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ec3ca694665f..e890d2d4ec89 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -63,6 +63,10 @@ static bool __read_mostly tracing_selftest_running; */ bool __read_mostly tracing_selftest_disabled; +/* Pipe tracepoints to printk */ +struct trace_iterator *tracepoint_print_iter; +int tracepoint_printk; + /* For tracers that don't implement custom flags */ static struct tracer_opt dummy_tracer_opt[] = { { } @@ -193,6 +197,13 @@ static int __init set_trace_boot_clock(char *str) } __setup("trace_clock=", set_trace_boot_clock); +static int __init set_tracepoint_printk(char *str) +{ + if ((strcmp(str, "=0") != 0 && strcmp(str, "=off") != 0)) + tracepoint_printk = 1; + return 1; +} +__setup("tp_printk", set_tracepoint_printk); unsigned long long ns2usecs(cycle_t nsec) { @@ -6878,6 +6889,12 @@ out: void __init trace_init(void) { + if (tracepoint_printk) { + tracepoint_print_iter = + kmalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL); + if (WARN_ON(!tracepoint_print_iter)) + tracepoint_printk = 0; + } tracer_alloc_buffers(); init_ftrace_syscalls(); trace_event_init(); diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index c138c149d6ef..8de48bac1ce2 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -1313,5 +1313,6 @@ void trace_event_init(void); static inline void __init trace_event_init(void) { } #endif +extern struct trace_iterator *tracepoint_print_iter; #endif /* _LINUX_KERNEL_TRACE_H */ diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index fd9deb0e03f0..9f7175a3df71 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -212,8 +212,40 @@ void *ftrace_event_buffer_reserve(struct ftrace_event_buffer *fbuffer, } EXPORT_SYMBOL_GPL(ftrace_event_buffer_reserve); +static DEFINE_SPINLOCK(tracepoint_iter_lock); + +static void output_printk(struct ftrace_event_buffer *fbuffer) +{ + struct ftrace_event_call *event_call; + struct trace_event *event; + unsigned long flags; + struct trace_iterator *iter = tracepoint_print_iter; + + if (!iter) + return; + + event_call = fbuffer->ftrace_file->event_call; + if (!event_call || !event_call->event.funcs || + !event_call->event.funcs->trace) + return; + + event = &fbuffer->ftrace_file->event_call->event; + + spin_lock_irqsave(&tracepoint_iter_lock, flags); + trace_seq_init(&iter->seq); + iter->ent = fbuffer->entry; + event_call->event.funcs->trace(iter, 0, event); + trace_seq_putc(&iter->seq, 0); + printk("%s", iter->seq.buffer); + + spin_unlock_irqrestore(&tracepoint_iter_lock, flags); +} + void ftrace_event_buffer_commit(struct ftrace_event_buffer *fbuffer) { + if (tracepoint_printk) + output_printk(fbuffer); + event_trigger_unlock_commit(fbuffer->ftrace_file, fbuffer->buffer, fbuffer->event, fbuffer->entry, fbuffer->flags, fbuffer->pc); -- 2.1.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/