The patch titled
Subject: bug: set warn variable before calling WARN()
has been added to the -mm tree. Its filename is
bug-set-warn-variable-before-calling-warn.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/bug-set-warn-variable-before-calling-warn.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/bug-set-warn-variable-before-calling-warn.patch
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------------------------------------------------------
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
bug-set-warn-variable-before-calling-warn.patch
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