From b3568787820faf58fd5429a6a392b555e6b2ae82 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Fri, 26 Nov 2010 13:42:47 +0100 Subject: [PATCH] printk: Fix wake_up_klogd() vs cpu hotplug commit 49f4138346b3cec2706adff02658fe27ceb1e46f upstream. wake_up_klogd() may get called from preemptible context but uses __raw_get_cpu_var() to write to a per cpu variable. If it gets preempted between getting the address and writing to it, the cpu in question could be offline if the process gets scheduled back and hence writes to the per cpu data of an offline cpu. This buggy behaviour was introduced with fa33507a "printk: robustify printk, fix #2" which was supposed to fix a "using smp_processor_id() in preemptible" warning. Let's use this_cpu_write() instead which disables preemption and makes sure that the outlined scenario cannot happen. Signed-off-by: Heiko Carstens Acked-by: Eric Dumazet Signed-off-by: Peter Zijlstra LKML-Reference: <20101126124247.GC7023@osiris.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/printk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/printk.c b/kernel/printk.c index faa9f5915480..44a2aa76baa4 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -1070,7 +1070,7 @@ int printk_needs_cpu(int cpu) void wake_up_klogd(void) { if (waitqueue_active(&log_wait)) - __raw_get_cpu_var(printk_pending) = 1; + this_cpu_write(printk_pending, 1); } /** -- 2.34.1