Tracing updates for 5.8:

No new features this release. Mostly clean ups, restructuring and
 documentation.
 
  - Have ftrace_bug() show ftrace errors before the WARN, as the WARN will
    reboot the box before the error messages are printed if panic_on_warn
    is set.
 
  - Have traceoff_on_warn disable tracing sooner (before prints)
 
  - Write a message to the trace buffer that its being disabled when
    disable_trace_on_warning() is set.
 
  - Separate out synthetic events from histogram code to let it be used by
    other parts of the kernel.
 
  - More documentation on histogram design.
 
  - Other small fixes and clean ups.
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Merge tag 'trace-v5.8' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "No new features this release. Mostly clean ups, restructuring and
  documentation.

   - Have ftrace_bug() show ftrace errors before the WARN, as the WARN
     will reboot the box before the error messages are printed if
     panic_on_warn is set.

   - Have traceoff_on_warn disable tracing sooner (before prints)

   - Write a message to the trace buffer that its being disabled when
     disable_trace_on_warning() is set.

   - Separate out synthetic events from histogram code to let it be used
     by other parts of the kernel.

   - More documentation on histogram design.

   - Other small fixes and clean ups"

* tag 'trace-v5.8' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Remove obsolete PREEMPTIRQ_EVENTS kconfig option
  tracing/doc: Fix ascii-art in histogram-design.rst
  tracing: Add a trace print when traceoff_on_warning is triggered
  ftrace,bug: Improve traceoff_on_warn
  selftests/ftrace: Distinguish between hist and synthetic event checks
  tracing: Move synthetic events to a separate file
  tracing: Fix events.rst section numbering
  tracing/doc: Fix typos in histogram-design.rst
  tracing: Add hist_debug trace event files for histogram debugging
  tracing: Add histogram-design document
  tracing: Check state.disabled in synth event trace functions
  tracing/probe: reverse arguments to list_add
  tools/bootconfig: Add a summary of test cases and return error
  ftrace: show debugging information when panic_on_warn set

kernel/trace/Kconfig

@@ -249,15 +249,6 @@ config TRACE_PREEMPT_TOGGLE
 	  Enables hooks which will be called when preemption is first disabled,
 	  and last enabled.
 
-config PREEMPTIRQ_EVENTS
-	bool "Enable trace events for preempt and irq disable/enable"
-	select TRACE_IRQFLAGS
-	select TRACE_PREEMPT_TOGGLE if PREEMPTION
-	select GENERIC_TRACER
-	default n
-	help
-	  Enable tracing of disable and enable events for preemption and irqs.
-
 config IRQSOFF_TRACER
 	bool "Interrupts-off Latency Tracer"
 	default n
@@ -614,12 +605,30 @@ config TRACING_MAP
 	  generally used outside of that context, and is normally
 	  selected by tracers that use it.
 
+config SYNTH_EVENTS
+	bool "Synthetic trace events"
+	select TRACING
+	select DYNAMIC_EVENTS
+	default n
+	help
+	  Synthetic events are user-defined trace events that can be
+	  used to combine data from other trace events or in fact any
+	  data source.  Synthetic events can be generated indirectly
+	  via the trace() action of histogram triggers or directly
+	  by way of an in-kernel API.
+
+	  See Documentation/trace/events.rst or
+	  Documentation/trace/histogram.rst for details and examples.
+
+	  If in doubt, say N.
+
 config HIST_TRIGGERS
 	bool "Histogram triggers"
 	depends on ARCH_HAVE_NMI_SAFE_CMPXCHG
 	select TRACING_MAP
 	select TRACING
 	select DYNAMIC_EVENTS
+	select SYNTH_EVENTS
 	default n
 	help
 	  Hist triggers allow one or more arbitrary trace event fields
@@ -815,7 +824,7 @@ config PREEMPTIRQ_DELAY_TEST
 
 config SYNTH_EVENT_GEN_TEST
 	tristate "Test module for in-kernel synthetic event generation"
-	depends on HIST_TRIGGERS
+	depends on SYNTH_EVENTS
 	help
           This option creates a test module to check the base
           functionality of in-kernel synthetic event definition and
@@ -838,6 +847,29 @@ config KPROBE_EVENT_GEN_TEST
 
 	  If unsure, say N.
 
+config HIST_TRIGGERS_DEBUG
+	bool "Hist trigger debug support"
+	depends on HIST_TRIGGERS
+	help
+          Add "hist_debug" file for each event, which when read will
+          dump out a bunch of internal details about the hist triggers
+          defined on that event.
+
+          The hist_debug file serves a couple of purposes:
+
+            - Helps developers verify that nothing is broken.
+
+            - Provides educational information to support the details
+              of the hist trigger internals as described by
+              Documentation/trace/histogram-design.rst.
+
+          The hist_debug output only covers the data structures
+          related to the histogram definitions themselves and doesn't
+          display the internals of map buckets or variable values of
+          running histograms.
+
+          If unsure, say N.
+
 endif # FTRACE
 
 endif # TRACING_SUPPORT

kernel/trace/Makefile

@@ -72,6 +72,7 @@ endif
 obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
 obj-$(CONFIG_EVENT_TRACING) += trace_events_trigger.o
 obj-$(CONFIG_TRACE_EVENT_INJECT) += trace_events_inject.o
+obj-$(CONFIG_SYNTH_EVENTS) += trace_events_synth.o
 obj-$(CONFIG_HIST_TRIGGERS) += trace_events_hist.o
 obj-$(CONFIG_BPF_EVENTS) += bpf_trace.o
 obj-$(CONFIG_KPROBE_EVENTS) += trace_kprobe.o

kernel/trace/ftrace.c

@@ -2016,14 +2016,14 @@ void ftrace_bug(int failed, struct dyn_ftrace *rec)
 {
 	unsigned long ip = rec ? rec->ip : 0;
 
+	pr_info("------------[ ftrace bug ]------------\n");
+
 	switch (failed) {
 	case -EFAULT:
-		FTRACE_WARN_ON_ONCE(1);
 		pr_info("ftrace faulted on modifying ");
 		print_ip_sym(KERN_INFO, ip);
 		break;
 	case -EINVAL:
-		FTRACE_WARN_ON_ONCE(1);
 		pr_info("ftrace failed to modify ");
 		print_ip_sym(KERN_INFO, ip);
 		print_ip_ins(" actual:   ", (unsigned char *)ip);
@@ -2034,12 +2034,10 @@ void ftrace_bug(int failed, struct dyn_ftrace *rec)
 		}
 		break;
 	case -EPERM:
-		FTRACE_WARN_ON_ONCE(1);
 		pr_info("ftrace faulted on writing ");
 		print_ip_sym(KERN_INFO, ip);
 		break;
 	default:
-		FTRACE_WARN_ON_ONCE(1);
 		pr_info("ftrace faulted on unknown error ");
 		print_ip_sym(KERN_INFO, ip);
 	}
@@ -2066,6 +2064,8 @@ void ftrace_bug(int failed, struct dyn_ftrace *rec)
 		ip = ftrace_get_addr_curr(rec);
 		pr_cont("\n expected tramp: %lx\n", ip);
 	}
+
+	FTRACE_WARN_ON_ONCE(1);
 }
 
 static int ftrace_check_record(struct dyn_ftrace *rec, bool enable, bool update)

kernel/trace/trace.c

@@ -1299,8 +1299,11 @@ EXPORT_SYMBOL_GPL(tracing_off);
 
 void disable_trace_on_warning(void)
 {
-	if (__disable_trace_on_warning)
+	if (__disable_trace_on_warning) {
+		trace_array_printk_buf(global_trace.array_buffer.buffer, _THIS_IP_,
+			"Disabling tracing due to warning\n");
 		tracing_off();
+	}
 }
 
 /**

kernel/trace/trace.h

@@ -1661,6 +1661,7 @@ extern struct list_head ftrace_events;
 
 extern const struct file_operations event_trigger_fops;
 extern const struct file_operations event_hist_fops;
+extern const struct file_operations event_hist_debug_fops;
 extern const struct file_operations event_inject_fops;
 
 #ifdef CONFIG_HIST_TRIGGERS

kernel/trace/trace_events.c

@@ -2208,6 +2208,10 @@ event_create_dir(struct dentry *parent, struct trace_event_file *file)
 #ifdef CONFIG_HIST_TRIGGERS
 	trace_create_file("hist", 0444, file->dir, file,
 			  &event_hist_fops);
+#endif
+#ifdef CONFIG_HIST_TRIGGERS_DEBUG
+	trace_create_file("hist_debug", 0444, file->dir, file,
+			  &event_hist_debug_fops);
 #endif
 	trace_create_file("format", 0444, file->dir, call,
 			  &ftrace_event_format_fops);

kernel/trace/trace_probe.c

@@ -1006,7 +1006,7 @@ int trace_probe_init(struct trace_probe *tp, const char *event,
 	INIT_LIST_HEAD(&tp->event->class.fields);
 	INIT_LIST_HEAD(&tp->event->probes);
 	INIT_LIST_HEAD(&tp->list);
-	list_add(&tp->event->probes, &tp->list);
+	list_add(&tp->list, &tp->event->probes);
 
 	call = trace_probe_event_call(tp);
 	call->class = &tp->event->class;

kernel/trace/trace_synth.h

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef __TRACE_SYNTH_H
+#define __TRACE_SYNTH_H
+
+#include "trace_dynevent.h"
+
+#define SYNTH_SYSTEM		"synthetic"
+#define SYNTH_FIELDS_MAX	32
+
+#define STR_VAR_LEN_MAX		32 /* must be multiple of sizeof(u64) */
+
+struct synth_field {
+	char *type;
+	char *name;
+	size_t size;
+	unsigned int offset;
+	bool is_signed;
+	bool is_string;
+};
+
+struct synth_event {
+	struct dyn_event			devent;
+	int					ref;
+	char					*name;
+	struct synth_field			**fields;
+	unsigned int				n_fields;
+	unsigned int				n_u64;
+	struct trace_event_class		class;
+	struct trace_event_call			call;
+	struct tracepoint			*tp;
+	struct module				*mod;
+};
+
+extern struct synth_event *find_synth_event(const char *name);
+
+#endif /* __TRACE_SYNTH_H */

lib/bug.c

@@ -47,6 +47,7 @@
 #include <linux/bug.h>
 #include <linux/sched.h>
 #include <linux/rculist.h>
+#include <linux/ftrace.h>
 
 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
 
@@ -153,6 +154,8 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 	if (!bug)
 		return BUG_TRAP_TYPE_NONE;
 
+	disable_trace_on_warning();
+
 	file = NULL;
 	line = 0;
 	warning = 0;

tools/bootconfig/test-bootconfig.sh

@@ -124,9 +124,16 @@ for i in samples/good-* ; do
   xpass $BOOTCONF -a $i $INITRD
 done
 
+
+echo
+echo "=== Summary ==="
+echo "# of Passed: $(expr $NO - $NG - 1)"
+echo "# of Failed: $NG"
+
 echo
 if [ $NG -eq 0 ]; then
 	echo "All tests passed"
 else
 	echo "$NG tests failed"
+	exit 1
 fi

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-field-variable-support.tc

@@ -17,6 +17,11 @@ if [ ! -f synthetic_events ]; then
     exit_unsupported
 fi
 
+if [ ! -f events/sched/sched_process_fork/hist ]; then
+    echo "hist trigger is not supported"
+    exit_unsupported
+fi
+
 echo "Test field variable support"
 
 echo 'wakeup_latency u64 lat; pid_t pid; int prio; char comm[16]' > synthetic_events

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-inter-event-combined-hist.tc

@@ -17,6 +17,11 @@ if [ ! -f synthetic_events ]; then
     exit_unsupported
 fi
 
+if [ ! -f events/sched/sched_process_fork/hist ]; then
+    echo "hist trigger is not supported"
+    exit_unsupported
+fi
+
 echo "Test create synthetic event"
 
 echo 'waking_latency  u64 lat pid_t pid' > synthetic_events

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-multi-actions-accept.tc

@@ -17,6 +17,11 @@ if [ ! -f synthetic_events ]; then
     exit_unsupported
 fi
 
+if [ ! -f events/sched/sched_process_fork/hist ]; then
+    echo "hist trigger is not supported"
+    exit_unsupported
+fi
+
 echo "Test multiple actions on hist trigger"
 echo 'wakeup_latency u64 lat; pid_t pid' >> synthetic_events
 TRIGGER1=events/sched/sched_wakeup/trigger

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmatch-action-hist.tc

@@ -17,6 +17,11 @@ if [ ! -f synthetic_events ]; then
     exit_unsupported
 fi
 
+if [ ! -f events/sched/sched_process_fork/hist ]; then
+    echo "hist trigger is not supported"
+    exit_unsupported
+fi
+
 echo "Test create synthetic event"
 
 echo 'wakeup_latency  u64 lat pid_t pid char comm[16]' > synthetic_events

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmatch-onmax-action-hist.tc

@@ -17,6 +17,11 @@ if [ ! -f synthetic_events ]; then
     exit_unsupported
 fi
 
+if [ ! -f events/sched/sched_process_fork/hist ]; then
+    echo "hist trigger is not supported"
+    exit_unsupported
+fi
+
 echo "Test create synthetic event"
 
 echo 'wakeup_latency  u64 lat pid_t pid char comm[16]' > synthetic_events

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmax-action-hist.tc

@@ -17,6 +17,11 @@ if [ ! -f synthetic_events ]; then
     exit_unsupported
 fi
 
+if [ ! -f events/sched/sched_process_fork/hist ]; then
+    echo "hist trigger is not supported"
+    exit_unsupported
+fi
+
 echo "Test create synthetic event"
 
 echo 'wakeup_latency  u64 lat pid_t pid char comm[16]' > synthetic_events

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-snapshot-action-hist.tc

@@ -12,6 +12,11 @@ if [ ! -f set_event ]; then
     exit_unsupported
 fi
 
+if [ ! -f events/sched/sched_process_fork/hist ]; then
+    echo "hist trigger is not supported"
+    exit_unsupported
+fi
+
 if [ ! -f snapshot ]; then
     echo "snapshot is not supported"
     exit_unsupported

tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-trace-action-hist.tc

@@ -17,6 +17,11 @@ if [ ! -f synthetic_events ]; then
     exit_unsupported
 fi
 
+if [ ! -f events/sched/sched_process_fork/hist ]; then
+    echo "hist trigger is not supported"
+    exit_unsupported
+fi
+
 grep -q "trace(<synthetic_event>" README || exit_unsupported # version issue
 
 echo "Test create synthetic event"