This contains a few fixes and a clean up.

- A bad merge caused an "endif" to go in the wrong place in
      scripts/Makefile.build
  - Softirq tracing fix for tracing that corrupts lockdep and causes a false
      splat
  - Histogram documentation typo fixes
  - Fix a bad memory reference when passing in no filter to the filter code
  - Simplify code by using the swap macro instead of open coding the swap
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Merge tag 'trace-v4.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:
 "This contains a few fixes and a clean up.

   - a bad merge caused an "endif" to go in the wrong place in
     scripts/Makefile.build

   - softirq tracing fix for tracing that corrupts lockdep and causes a
     false splat

   - histogram documentation typo fixes

   - fix a bad memory reference when passing in no filter to the filter
     code

   - simplify code by using the swap macro instead of open coding the
     swap"

* tag 'trace-v4.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Fix SKIP_STACK_VALIDATION=1 build due to bad merge with -mrecord-mcount
  tracing: Fix some errors in histogram documentation
  tracing: Use swap macro in update_max_tr
  softirq: Reorder trace_softirqs_on to prevent lockdep splat
  tracing: Check for no filter when processing event filters

Documentation/trace/histogram.txt

@@ -1729,35 +1729,35 @@ If a variable isn't a key variable or prefixed with 'vals=', the
 associated event field will be saved in a variable but won't be summed
 as a value:
 
-  # echo 'hist:keys=next_pid:ts1=common_timestamp ... >> event/trigger
+  # echo 'hist:keys=next_pid:ts1=common_timestamp ...' >> event/trigger
 
 Multiple variables can be assigned at the same time.  The below would
 result in both ts0 and b being created as variables, with both
 common_timestamp and field1 additionally being summed as values:
 
-  # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ... >> \
+  # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ...' >> \
 	event/trigger
 
 Note that variable assignments can appear either preceding or
 following their use.  The command below behaves identically to the
 command above:
 
-  # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ... >> \
+  # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ...' >> \
 	event/trigger
 
 Any number of variables not bound to a 'vals=' prefix can also be
 assigned by simply separating them with colons.  Below is the same
 thing but without the values being summed in the histogram:
 
-  # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ... >> event/trigger
+  # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ...' >> event/trigger
 
 Variables set as above can be referenced and used in expressions on
 another event.
 
 For example, here's how a latency can be calculated:
 
-  # echo 'hist:keys=pid,prio:ts0=common_timestamp ... >> event1/trigger
+  # echo 'hist:keys=pid,prio:ts0=common_timestamp ...' >> event1/trigger
-  # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ... >> event2/trigger
+  # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...' >> event2/trigger
 
 In the first line above, the event's timetamp is saved into the
 variable ts0.  In the next line, ts0 is subtracted from the second
@@ -1766,7 +1766,7 @@ yet another variable, 'wakeup_lat'.  The hist trigger below in turn
 makes use of the wakeup_lat variable to compute a combined latency
 using the same key and variable from yet another event:
 
-  # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ... >> event3/trigger
+  # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ...' >> event3/trigger
 
 2.2.2 Synthetic Events
 ----------------------
@@ -1807,10 +1807,11 @@ the command that defined it with a '!':
 At this point, there isn't yet an actual 'wakeup_latency' event
 instantiated in the event subsytem - for this to happen, a 'hist
 trigger action' needs to be instantiated and bound to actual fields
-and variables defined on other events (see Section 6.3.3 below).
+and variables defined on other events (see Section 2.2.3 below on
+how that is done using hist trigger 'onmatch' action). Once that is
+done, the 'wakeup_latency' synthetic event instance is created.
 
-Once that is done, an event instance is created, and a histogram can
+A histogram can now be defined for the new synthetic event:
-be defined using it:
 
   # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
         /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
@@ -1960,7 +1961,7 @@ hist trigger specification.
     back to that pid, the timestamp difference is calculated.  If the
     resulting latency, stored in wakeup_lat, exceeds the current
     maximum latency, the values specified in the save() fields are
-    recoreded:
+    recorded:
 
     # echo 'hist:keys=pid:ts0=common_timestamp.usecs \
             if comm=="cyclictest"' >> \

kernel/softirq.c

@@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned int cnt)
 {
 	lockdep_assert_irqs_disabled();
 
+	if (preempt_count() == cnt)
+		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
+
 	if (softirq_count() == (cnt & SOFTIRQ_MASK))
 		trace_softirqs_on(_RET_IP_);
-	preempt_count_sub(cnt);
+
+	__preempt_count_sub(cnt);
 }
 
 /*

kernel/trace/trace.c

@@ -1360,8 +1360,6 @@ __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 void
 update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 {
-	struct ring_buffer *buf;
-
 	if (tr->stop_count)
 		return;
 
@@ -1375,9 +1373,7 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 
 	arch_spin_lock(&tr->max_lock);
 
-	buf = tr->trace_buffer.buffer;
+	swap(tr->trace_buffer.buffer, tr->max_buffer.buffer);
-	tr->trace_buffer.buffer = tr->max_buffer.buffer;
-	tr->max_buffer.buffer = buf;
 
 	__update_max_tr(tr, tsk, cpu);
 	arch_spin_unlock(&tr->max_lock);

kernel/trace/trace_events_filter.c

@@ -78,7 +78,8 @@ static const char * ops[] = { OPS };
 	C(TOO_MANY_PREDS,	"Too many terms in predicate expression"), \
 	C(INVALID_FILTER,	"Meaningless filter expression"),	\
 	C(IP_FIELD_ONLY,	"Only 'ip' field is supported for function trace"), \
-	C(INVALID_VALUE,	"Invalid value (did you forget quotes)?"),
+	C(INVALID_VALUE,	"Invalid value (did you forget quotes)?"), \
+	C(NO_FILTER,		"No filter found"),
 
 #undef C
 #define C(a, b)		FILT_ERR_##a
@@ -550,6 +551,13 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
 		goto out_free;
 	}
 
+	if (!N) {
+		/* No program? */
+		ret = -EINVAL;
+		parse_error(pe, FILT_ERR_NO_FILTER, ptr - str);
+		goto out_free;
+	}
+
 	prog[N].pred = NULL;					/* #13 */
 	prog[N].target = 1;		/* TRUE */
 	prog[N+1].pred = NULL;

scripts/Makefile.build

@@ -239,6 +239,7 @@ cmd_record_mcount =						\
 	     "$(CC_FLAGS_FTRACE)" ]; then			\
 		$(sub_cmd_record_mcount)			\
 	fi;
+endif # -record-mcount
 endif # CONFIG_FTRACE_MCOUNT_RECORD
 
 ifdef CONFIG_STACK_VALIDATION
@@ -263,7 +264,6 @@ ifneq ($(RETPOLINE_CFLAGS),)
   objtool_args += --retpoline
 endif
 endif
-endif
 
 
 ifdef CONFIG_MODVERSIONS