linux-kernel - [RFC patch 16/41] tracing: Remove the ULONG

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Date:   Wed, 10 Apr 2019 12:28:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexander Potapenko <glider@...gle.com>
Subject: [RFC patch 16/41] tracing: Remove the ULONG_MAX stack trace hackery

No architecture terminates the stack trace with ULONG_MAX anymore. As the
code checks the number of entries stored anyway there is no point in
keeping all that ULONG_MAX magic around.

The histogram code zeroes the storage before saving the stack, so if the
trace is shorter than the maximum number of entries it can terminate the
print loop if a zero entry is detected.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/trace/trace_events_hist.c |    2 +-
 kernel/trace/trace_stack.c       |   20 +++++---------------
 2 files changed, 6 insertions(+), 16 deletions(-)

--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5246,7 +5246,7 @@ static void hist_trigger_stacktrace_prin
 	unsigned int i;
 
 	for (i = 0; i < max_entries; i++) {
-		if (stacktrace_entries[i] == ULONG_MAX)
+		if (!stacktrace_entries[i])
 			return;
 
 		seq_printf(m, "%*c", 1 + spaces, ' ');
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -18,8 +18,7 @@
 
 #include "trace.h"
 
-static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
-	 { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
+static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES + 1];
 unsigned stack_trace_index[STACK_TRACE_ENTRIES];
 
 /*
@@ -52,10 +51,7 @@ void stack_trace_print(void)
 			   stack_trace_max.nr_entries);
 
 	for (i = 0; i < stack_trace_max.nr_entries; i++) {
-		if (stack_dump_trace[i] == ULONG_MAX)
-			break;
-		if (i+1 == stack_trace_max.nr_entries ||
-				stack_dump_trace[i+1] == ULONG_MAX)
+		if (i + 1 == stack_trace_max.nr_entries)
 			size = stack_trace_index[i];
 		else
 			size = stack_trace_index[i] - stack_trace_index[i+1];
@@ -150,8 +146,6 @@ check_stack(unsigned long ip, unsigned l
 		p = start;
 
 		for (; p < top && i < stack_trace_max.nr_entries; p++) {
-			if (stack_dump_trace[i] == ULONG_MAX)
-				break;
 			/*
 			 * The READ_ONCE_NOCHECK is used to let KASAN know that
 			 * this is not a stack-out-of-bounds error.
@@ -183,8 +177,6 @@ check_stack(unsigned long ip, unsigned l
 	}
 
 	stack_trace_max.nr_entries = x;
-	for (; x < i; x++)
-		stack_dump_trace[x] = ULONG_MAX;
 
 	if (task_stack_end_corrupted(current)) {
 		stack_trace_print();
@@ -286,7 +278,7 @@ static void *
 {
 	long n = *pos - 1;
 
-	if (n >= stack_trace_max.nr_entries || stack_dump_trace[n] == ULONG_MAX)
+	if (n >= stack_trace_max.nr_entries)
 		return NULL;
 
 	m->private = (void *)n;
@@ -360,12 +352,10 @@ static int t_show(struct seq_file *m, vo
 
 	i = *(long *)v;
 
-	if (i >= stack_trace_max.nr_entries ||
-	    stack_dump_trace[i] == ULONG_MAX)
+	if (i >= stack_trace_max.nr_entries)
 		return 0;
 
-	if (i+1 == stack_trace_max.nr_entries ||
-	    stack_dump_trace[i+1] == ULONG_MAX)
+	if (i + 1 == stack_trace_max.nr_entries)
 		size = stack_trace_index[i];
 	else
 		size = stack_trace_index[i] - stack_trace_index[i+1];