linux-kernel - Re: [PATCH] module: Prevent recursion bug caused by module RCU check

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Message-ID: <20151020170905.GV11639@twins.programming.kicks-ass.net>
Date:	Tue, 20 Oct 2015 19:09:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] module: Prevent recursion bug caused by module RCU check

On Tue, Oct 20, 2015 at 06:53:31PM +0200, Peter Zijlstra wrote:
> Also, would it not be better to fix WARN_ON_ONCE() instead?
> 

Clearly I'm an idiot and should stay away from the computer...

---
 include/asm-generic/bug.h | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 630dd2372238..d0972fc8433f 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -110,9 +110,10 @@ extern void warn_slowpath_null(const char *file, const int line);
 	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 char *file, const int line);
 	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);				\
 })
 
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