From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: linux-next: Tree for Feb 4 Date: Wed, 4 Feb 2015 17:51:44 -0800 Message-ID: <20150205015144.GT5370@linux.vnet.ibm.com> References: <20150204193535.58f132c5@canb.auug.org.au> <1511573.AlfExlvQsO@vostro.rjw.lan> <20150204215357.GL5370@linux.vnet.ibm.com> <11131483.LrRNxJumiL@vostro.rjw.lan> <20150204235115.GP5370@linux.vnet.ibm.com> <20150205001019.GA12362@linux.vnet.ibm.com> <20150205005716.GS5370@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e37.co.us.ibm.com ([32.97.110.158]:36868 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751798AbbBEBvu (ORCPT ); Wed, 4 Feb 2015 20:51:50 -0500 Received: from /spool/local by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 4 Feb 2015 18:51:49 -0700 Content-Disposition: inline In-Reply-To: Sender: linux-next-owner@vger.kernel.org List-ID: To: Sedat Dilek Cc: "Rafael J. Wysocki" , "Rafael J. Wysocki" , linux-next , LKML , Stephen Rothwell , Kristen Carlson Accardi , Dave Hansen , "H. Peter Anvin" , Rik van Riel , Mel Gorman On Thu, Feb 05, 2015 at 02:18:01AM +0100, Sedat Dilek wrote: > On Thu, Feb 5, 2015 at 1:57 AM, Paul E. McKenney > wrote: > > On Thu, Feb 05, 2015 at 01:30:45AM +0100, Sedat Dilek wrote: > >> On Thu, Feb 5, 2015 at 1:10 AM, Paul E. McKenney > >> 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] [] dump_stack+0x4c/0x65 > >> >> > > > > [ 1144.486104] [] 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 :-) > > > > Sorry! Actually, getting results tomorrow would be plenty OK by me. > > > >> 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... > > > > As expected. The trace can still appear, but the outgoing CPU needs to > > be delayed by at least one jiffy on its final pass through the idle loop. > > Which can really happen in virtualized environments. > > > >> [ 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. > > > > Looking forward to seeing the results! > > > > Thanx, Paul > > > >> - 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 > >> > Signed-off-by: Paul E. McKenney > >> > > >> > 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); > >> > } > >> > } > >> > > >> > > > > [ CC involved people of "culprit" commit ] > > OK, this fixes the issue for me. > ( Several s/r and offline/online cpu1. ) Very good > I looked through the commits and the problem seems to be introduced with... > > commit d17d8f9dedb9dd76fd540a5c497101529d9eb25a > "x86/mm: Add tracepoints for TLB flushes" > > Can you please add a Fixes-tag? > > Fixes: d17d8f9dedb9 ("x86/mm: Add tracepoints for TLB flushes") Done! > And maybe label your proposal-patch with "x86/mm:" instead of "x86:"? > > Feel free to add my Tested-by. Also done! > Anyway, we should listen to the voices of the involved people. Definitely -- this is but one way to fix this problem. It is the simplest, so it is the one that I am starting with, but if someone has a better idea, please don't keep it a secret! > Thanks, Paul! And many thanks for your testing efforts, especially your late-night testing efforts! Thanx, Paul > - Sedat - > > [1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d17d8f9dedb9dd76fd540a5c497101529d9eb25a >