On Wed, Feb 04, 2015 at 03:51:15PM -0800, Paul E. McKenney wrote: > On Wed, Feb 04, 2015 at 11:59:31PM +0100, Rafael J. Wysocki wrote: > > On Wednesday, February 04, 2015 01:53:58 PM Paul E. McKenney wrote: > > > On Wed, Feb 04, 2015 at 10:54:07PM +0100, Rafael J. Wysocki wrote: > > > > On Wednesday, February 04, 2015 09:18:03 PM Sedat Dilek wrote: [ . . . ] > > > > > [ 1144.482666] Disabling non-boot CPUs ... > > > > > [ 1144.483000] intel_pstate CPU 1 exiting > > > > > [ 1144.486064] > > > > > [ 1144.486065] =============================== > > > > > [ 1144.486067] smpboot: CPU 1 didn't die... > > > > > [ 1144.486067] [ INFO: suspicious RCU usage. ] > > > > > [ 1144.486069] 3.19.0-rc7-next-20150204.1-iniza-small #1 Not tainted > > > > > [ 1144.486070] ------------------------------- > > > > > [ 1144.486072] include/trace/events/tlb.h:35 suspicious > > > > > rcu_dereference_check() usage! > > > > > [ 1144.486073] > > > > > [ 1144.486073] other info that might help us debug this: > > > > > [ 1144.486073] > > > > > [ 1144.486074] > > > > > [ 1144.486074] RCU used illegally from offline CPU! > > > > > [ 1144.486074] rcu_scheduler_active = 1, debug_locks = 0 > > > > > [ 1144.486076] no locks held by swapper/1/0. > > > > > [ 1144.486076] > > > > > [ 1144.486076] stack backtrace: > > > > > [ 1144.486079] CPU: 1 PID: 0 Comm: swapper/1 Not tainted > > > > > 3.19.0-rc7-next-20150204.1-iniza-small #1 > > > > > [ 1144.486080] Hardware name: SAMSUNG ELECTRONICS CO., LTD. > > > > > 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013 > > > > > [ 1144.486085] 0000000000000001 ffff88011a44fe18 ffffffff817e370d > > > > > 0000000000000011 > > > > > [ 1144.486088] ffff88011a448290 ffff88011a44fe48 ffffffff810d6847 > > > > > ffff8800c66b9600 > > > > > [ 1144.486091] 0000000000000001 ffff88011a44c000 ffffffff81cb3900 > > > > > ffff88011a44fe78 > > > > > [ 1144.486092] Call Trace: > > > > > [ 1144.486099] [<ffffffff817e370d>] dump_stack+0x4c/0x65 > > > > > [ 1144.486104] [<ffffffff810d6847>] lockdep_rcu_suspicious+0xe7/0x120 > > > > > > As near as I can tell, idle_task_exit() is running on an offline CPU, > > > then calling switch_mm() which contains trace_tlb_flush(), which uses RCU. > > > And RCU is objecting to being used from a CPU that it is ignoring. > > > > > > One approach would be to push RCU's idea of when the CPU goes offline > > > down into arch code in this case, using some Kconfig symbol and > > > the usual conditional compilation. Another approach would be to > > > invoke the trace calls under cpu_online(), for example, for the > > > first such call in switch_mm(): > > > > > > if (cpu_online(smp_processor_id())) > > > trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); > > > > > > The compiler would discard this if tracing was disabled. > > > > That looks like less intrusive to me. > > One possible concern is increased context-switch path length, but that > would only be the case where tracing is enabled by default. Nevertheless, here is an untested patch. Does it help? Thanx, Paul ------------------------------------------------------------------------ x86: Omit switch_mm() tracing for offline CPUs The architecture-specific switch_mm() function can be called by offline CPUs, but includes event tracing, which cannot be legally carried out on offline CPUs. This results in a lockdep-RCU splat. This commit fixes this splat by omitting the tracing when the CPU is offline. Reported-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 40269a2bf6f9..7e7f2445fbc9 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -47,7 +47,8 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, /* Re-load page tables */ load_cr3(next->pgd); - trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); + if (cpu_online(smp_processor_id())) + trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); /* Stop flush ipis for the previous mm */ cpumask_clear_cpu(cpu, mm_cpumask(prev)); @@ -84,7 +85,8 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, * to make sure to use no freed page tables. */ load_cr3(next->pgd); - trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); + if (cpu_online(smp_processor_id())) + trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); load_LDT_nolock(&next->context); } } -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
