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authorHeiko Carstens <heiko.carstens@de.ibm.com>2010-11-26 13:42:47 +0100
committerIngo Molnar <mingo@elte.hu>2010-11-26 15:03:11 +0100
commit49f4138346b3cec2706adff02658fe27ceb1e46f (patch)
tree20259bf8196685766e8b4d3ae761102a0f635913
parentd5ad140bc1505a98c0f040937125bfcbb508078f (diff)
printk: Fix wake_up_klogd() vs cpu hotplug
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 <heiko.carstens@de.ibm.com> Acked-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20101126124247.GC7023@osiris.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/printk.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/printk.c b/kernel/printk.c
index 9a2264fc42ca..cf7588e93f6f 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1088,7 +1088,7 @@ 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);
}
/**