From 6d3321e8e2b3bf6a5892e2ef673c7bf536e3f904 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Thu, 23 Jun 2011 11:19:26 -0700 Subject: x86, mtrr: lock stop machine during MTRR rendezvous sequence MTRR rendezvous sequence using stop_one_cpu_nowait() can potentially happen in parallel with another system wide rendezvous using stop_machine(). This can lead to deadlock (The order in which works are queued can be different on different cpu's. Some cpu's will be running the first rendezvous handler and others will be running the second rendezvous handler. Each set waiting for the other set to join for the system wide rendezvous, leading to a deadlock). MTRR rendezvous sequence is not implemented using stop_machine() as this gets called both from the process context aswell as the cpu online paths (where the cpu has not come online and the interrupts are disabled etc). stop_machine() works with only online cpus. For now, take the stop_machine mutex in the MTRR rendezvous sequence that gets called from an online cpu (here we are in the process context and can potentially sleep while taking the mutex). And the MTRR rendezvous that gets triggered during cpu online doesn't need to take this stop_machine lock (as the stop_machine() already ensures that there is no cpu hotplug going on in parallel by doing get_online_cpus()) TBD: Pursue a cleaner solution of extending the stop_machine() infrastructure to handle the case where the calling cpu is still not online and use this for MTRR rendezvous sequence. fixes: https://bugzilla.novell.com/show_bug.cgi?id=672008 Reported-by: Vadim Kotelnikov Signed-off-by: Suresh Siddha Link: http://lkml.kernel.org/r/20110623182056.807230326@sbsiddha-MOBL3.sc.intel.com Cc: stable@kernel.org # 2.6.35+, backport a week or two after this gets more testing in mainline Signed-off-by: H. Peter Anvin --- arch/x86/kernel/cpu/mtrr/main.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) (limited to 'arch/x86/kernel/cpu/mtrr') diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c index 929739a653d1..3d17bc7f06e6 100644 --- a/arch/x86/kernel/cpu/mtrr/main.c +++ b/arch/x86/kernel/cpu/mtrr/main.c @@ -248,6 +248,25 @@ set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type typ unsigned long flags; int cpu; +#ifdef CONFIG_SMP + /* + * If this cpu is not yet active, we are in the cpu online path. There + * can be no stop_machine() in parallel, as stop machine ensures this + * by using get_online_cpus(). We can skip taking the stop_cpus_mutex, + * as we don't need it and also we can't afford to block while waiting + * for the mutex. + * + * If this cpu is active, we need to prevent stop_machine() happening + * in parallel by taking the stop cpus mutex. + * + * Also, this is called in the context of cpu online path or in the + * context where cpu hotplug is prevented. So checking the active status + * of the raw_smp_processor_id() is safe. + */ + if (cpu_active(raw_smp_processor_id())) + mutex_lock(&stop_cpus_mutex); +#endif + preempt_disable(); data.smp_reg = reg; @@ -330,6 +349,10 @@ set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type typ local_irq_restore(flags); preempt_enable(); +#ifdef CONFIG_SMP + if (cpu_active(raw_smp_processor_id())) + mutex_unlock(&stop_cpus_mutex); +#endif } /** -- cgit v1.2.3