From d150a2b96558a7349cbf3a72a279c37bc67d50fb Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Tue, 20 Apr 2010 10:38:10 -0400 Subject: [PATCH] module: fix __module_ref_addr() The __module_ref_addr() problem disappears in 2.6.34-rc kernels because these percpu accesses were re-factored. __module_ref_addr() should use per_cpu_ptr() to obfuscate the pointer (RELOC_HIDE is needed for per cpu pointers). This non-standard per-cpu pointer use has been introduced by commit 720eba31f47aeade8ec130ca7f4353223c49170f It causes a NULL pointer exception on some configurations when CONFIG_TRACING is enabled on 2.6.33. This patch fixes the problem (acknowledged by Randy who reported the bug). It did not appear to hurt previously because most of the accesses were done through local_inc, which probably obfuscated the access enough that no compiler optimizations were done. But with local_read() done when CONFIG_TRACING is active, this becomes a problem. Non-CONFIG_TRACING is probably affected as well (module.c contains local_set and local_read that use __module_ref_addr()), but I guess nobody noticed because we've been lucky enough that the compiler did not generate the inappropriate optimization pattern there. This patch should be queued for the 2.6.29.x through 2.6.33.x stable branches. (tested on 2.6.33.1 x86_64) Signed-off-by: Mathieu Desnoyers Tested-by: Randy Dunlap CC: Eric Dumazet CC: Rusty Russell CC: Peter Zijlstra CC: Tejun Heo CC: Ingo Molnar CC: Andrew Morton CC: Linus Torvalds CC: Greg Kroah-Hartman CC: Steven Rostedt Signed-off-by: Greg Kroah-Hartman --- include/linux/module.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/module.h b/include/linux/module.h index 482efc865acf..460df152964d 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -455,7 +455,7 @@ void symbol_put_addr(void *addr); static inline local_t *__module_ref_addr(struct module *mod, int cpu) { #ifdef CONFIG_SMP - return (local_t *) (mod->refptr + per_cpu_offset(cpu)); + return (local_t *) per_cpu_ptr(mod->refptr, cpu); #else return &mod->ref; #endif -- 2.34.1