Messages in this thread Patch in this message | | | Date | Tue, 20 Oct 2015 18:53:31 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] module: Prevent recursion bug caused by module RCU check |
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On Tue, Oct 20, 2015 at 06:39:52PM +0200, Peter Zijlstra wrote: > On Tue, Oct 20, 2015 at 12:21:03PM -0400, Steven Rostedt wrote: > > +++ b/kernel/module.c > > @@ -284,11 +284,25 @@ static void module_assert_mutex(void) > > static void module_assert_mutex_or_preempt(void) > > { > > #ifdef CONFIG_LOCKDEP > > + static int once; > > + > > if (unlikely(!debug_locks)) > > return; > > > > - WARN_ON(!rcu_read_lock_sched_held() && > > - !lockdep_is_held(&module_mutex)); > > + /* > > + * Would be nice to use WARN_ON_ONCE(), but the warning > > + * that causes a stack trace may call __module_address() > > + * which may call here, and we trigger the warning again, > > + * before the WARN_ON_ONCE() updates its flag. > > + * To prevent the recursion, we need to open code the > > + * once logic. > > + */ > > + if (!once && > > + unlikely(!rcu_read_lock_sched_held() && > > + !lockdep_is_held(&module_mutex))) { > > + once++; > > once = 1; > > is more 'once' :-) Otherwise its once every 4-odd billion. > > > + WARN_ON(1); > > + } > > #endif
Also, would it not be better to fix WARN_ON_ONCE() instead?
--- include/asm-generic/bug.h | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h index 630dd2372238..c41e698613f3 100644 --- a/include/asm-generic/bug.h +++ b/include/asm-generic/bug.h @@ -110,9 +110,11 @@ 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)) \ + if (unlikely(__ret_warn_once)) { \ + if (!__warned) \ __warned = true; \ + WARN_ON(1); \ + } \ unlikely(__ret_warn_once); \ }) @@ -120,9 +122,11 @@ 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)) \ + if (unlikely(__ret_warn_once)) { \ + if (!__warned) \ __warned = true; \ + WARN(1, format); \ + } \ unlikely(__ret_warn_once); \ })
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