On Thu, Feb 5, 2015 at 1:10 AM, Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > 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? No bedtime :-) I tried with a revert of... commit 5f1dedac9adb6259bb7b62a923bd7c247a2f2d5b rcu: Handle outgoing CPUs on exit from idle loop ...and offlining cpu1 seems not to produce the trace... [ 115.280244] PPP BSD Compression module registered [ 115.288761] PPP Deflate Compression module registered [ 162.935524] intel_pstate CPU 1 exiting [ 162.949729] smpboot: CPU 1 is now offline Will try the patch. - Sedat - > > 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
