[merged] bug-set-warn-variable-before-calling-warn.patch removed from -mm tree

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The patch titled
     Subject: bug: set warn variable before calling WARN()
has been removed from the -mm tree.  Its filename was
     bug-set-warn-variable-before-calling-warn.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Steven Rostedt <rostedt@xxxxxxxxxxx>
Subject: bug: set warn variable before calling WARN()

This has hit me a couple of times already.  I would be debugging code and
the system would simply hang and then reboot.  Finally, I found that the
problem was caused by WARN_ON_ONCE() and friends.

The macro WARN_ON_ONCE(condition) is defined as:

	static bool __section(.data.unlikely) __warned;
	int __ret_warn_once = !!(condition);

	if (unlikely(__ret_warn_once))
		if (WARN_ON(!__warned))
			__warned = true;

	unlikely(__ret_warn_once);

Which looks great and all.  But what I have hit, is an issue when
WARN_ON() itself hits the same WARN_ON_ONCE() code.  Because, the variable
__warned is not yet set.  Then it too calls WARN_ON() and that triggers
the warning again.  It keeps doing this until the stack is overflowed and
the system crashes.

By setting __warned first before calling WARN_ON() makes the original
WARN_ON_ONCE() really only warn once, and not an infinite amount of times
if the WARN_ON() also triggers the warning.

Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 include/asm-generic/bug.h |   21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff -puN include/asm-generic/bug.h~bug-set-warn-variable-before-calling-warn include/asm-generic/bug.h
--- a/include/asm-generic/bug.h~bug-set-warn-variable-before-calling-warn
+++ a/include/asm-generic/bug.h
@@ -110,9 +110,10 @@ extern void warn_slowpath_null(const cha
 	static bool __section(.data.unlikely) __warned;		\
 	int __ret_warn_once = !!(condition);			\
 								\
-	if (unlikely(__ret_warn_once))				\
-		if (WARN_ON(!__warned)) 			\
-			__warned = true;			\
+	if (unlikely(__ret_warn_once && !__warned)) {		\
+		__warned = true;				\
+		WARN_ON(1);					\
+	}							\
 	unlikely(__ret_warn_once);				\
 })
 
@@ -120,9 +121,10 @@ extern void warn_slowpath_null(const cha
 	static bool __section(.data.unlikely) __warned;		\
 	int __ret_warn_once = !!(condition);			\
 								\
-	if (unlikely(__ret_warn_once))				\
-		if (WARN(!__warned, format)) 			\
-			__warned = true;			\
+	if (unlikely(__ret_warn_once && !__warned)) {		\
+		__warned = true;				\
+		WARN(1, format);				\
+	}							\
 	unlikely(__ret_warn_once);				\
 })
 
@@ -130,9 +132,10 @@ extern void warn_slowpath_null(const cha
 	static bool __section(.data.unlikely) __warned;		\
 	int __ret_warn_once = !!(condition);			\
 								\
-	if (unlikely(__ret_warn_once))				\
-		if (WARN_TAINT(!__warned, taint, format))	\
-			__warned = true;			\
+	if (unlikely(__ret_warn_once && !__warned)) {		\
+		__warned = true;				\
+		WARN_TAINT(1, taint, format);			\
+	}							\
 	unlikely(__ret_warn_once);				\
 })
 
_

Patches currently in -mm which might be from rostedt@xxxxxxxxxxx are


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