From 19d436268dde95389c616bb3819da73f0a8b28a8 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Sat, 25 Feb 2017 08:56:53 +0100
Subject: debug: Add _ONCE() logic to report_bug()

Josh suggested moving the _ONCE logic inside the trap handler, using a
bit in the bug_entry::flags field, avoiding the need for the extra
variable.

Sadly this only works for WARN_ON_ONCE(), since the others have
printk() statements prior to triggering the trap.

Still, this saves a fair amount of text and some data:

  text         data       filename
  10682460     4530992    defconfig-build/vmlinux.orig
  10665111     4530096    defconfig-build/vmlinux.patched

Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 lib/bug.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

(limited to 'lib')

diff --git a/lib/bug.c b/lib/bug.c
index 06edbbef0623..a6a1137d06db 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -47,7 +47,7 @@
 #include <linux/sched.h>
 #include <linux/rculist.h>
 
-extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
+extern struct bug_entry __start___bug_table[], __stop___bug_table[];
 
 static inline unsigned long bug_addr(const struct bug_entry *bug)
 {
@@ -62,10 +62,10 @@ static inline unsigned long bug_addr(const struct bug_entry *bug)
 /* Updates are protected by module mutex */
 static LIST_HEAD(module_bug_list);
 
-static const struct bug_entry *module_find_bug(unsigned long bugaddr)
+static struct bug_entry *module_find_bug(unsigned long bugaddr)
 {
 	struct module *mod;
-	const struct bug_entry *bug = NULL;
+	struct bug_entry *bug = NULL;
 
 	rcu_read_lock_sched();
 	list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
@@ -122,15 +122,15 @@ void module_bug_cleanup(struct module *mod)
 
 #else
 
-static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
+static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
 {
 	return NULL;
 }
 #endif
 
-const struct bug_entry *find_bug(unsigned long bugaddr)
+struct bug_entry *find_bug(unsigned long bugaddr)
 {
-	const struct bug_entry *bug;
+	struct bug_entry *bug;
 
 	for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 		if (bugaddr == bug_addr(bug))
@@ -141,9 +141,9 @@ const struct bug_entry *find_bug(unsigned long bugaddr)
 
 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 {
-	const struct bug_entry *bug;
+	struct bug_entry *bug;
 	const char *file;
-	unsigned line, warning;
+	unsigned line, warning, once, done;
 
 	if (!is_valid_bugaddr(bugaddr))
 		return BUG_TRAP_TYPE_NONE;
@@ -164,6 +164,18 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 		line = bug->line;
 #endif
 		warning = (bug->flags & BUGFLAG_WARNING) != 0;
+		once = (bug->flags & BUGFLAG_ONCE) != 0;
+		done = (bug->flags & BUGFLAG_DONE) != 0;
+
+		if (warning && once) {
+			if (done)
+				return BUG_TRAP_TYPE_WARN;
+
+			/*
+			 * Since this is the only store, concurrency is not an issue.
+			 */
+			bug->flags |= BUGFLAG_DONE;
+		}
 	}
 
 	if (warning) {
-- 
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