From dfbf2897d00499f94cd53a9806e697392cbfe6a3 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Thu, 17 Mar 2016 14:21:12 -0700 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 Acked-by: Peter Zijlstra (Intel) Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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..fdf6fa078422 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); \ }) @@ -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(1, taint, format); \ + } \ unlikely(__ret_warn_once); \ }) -- cgit v1.2.3-59-g8ed1b