Currently WARN_ONCE() and similar macros set __warned *after* calling the underlying macro. This risks infinite recursion if WARN_ONCE() is used to implement sanity tests in any code that can be called by printk.
This can be fixed by restructuring the macros to set __warned before calling further macros.
Signed-off-by: Daniel Thompson daniel.thompson@linaro.org ---
Notes: I discovered this problem when I temporarily added sanity tests to the irqflags macros during some of my development work but I suspect the scope is a little wider. I admit I was tempted to throw this change away after I had finished debugging but for two things prompted me to post it.
1. It did cost me a few minutes head scratching and I'd like to spare others the pain.
2. I realized the new code is potentially (and very fractionally) more efficient: the register containing address of __warned can be reused and a cache hit is a near certainty for the write.
Don't get too excited about the efficiency gains though they are extremely modest. Measures as code size benefit and using v4.0-rc4 the results are:
Kernel GCC version Code size reduction
arm multi_v7_defconfig Linaro 4.8-2014.01 224 bytes arm64 defconfig Linaro 4.9-2014.09 32 bytes i386_defconfig Redhat 4.9.2-6 62 bytes x86_64_defconfig Redhat 4.9.2-6 380 bytes
include/asm-generic/bug.h | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h index 630dd2372238..f8c8a819c563 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(true); \ + } \ 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(true, format); \ + } \ unlikely(__ret_warn_once); \ })
@@ -130,9 +132,10 @@ 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_TAINT(!__warned, taint, format)) \ - __warned = true; \ + if (unlikely(__ret_warn_once) && !__warned) { \ + __warned = true; \ + WARN_TAINT(true, taint, format); \ + } \ unlikely(__ret_warn_once); \ })
-- 2.1.0