Date:	Wed, 4 Feb 2015 20:13:17 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Sedat Dilek <sedat.dilek@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-next <linux-next@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Kristen Carlson Accardi <kristen@...ux.intel.com>,
	Dave Hansen <dave@...1.net>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>
Subject: Re: linux-next: Tree for Feb 4

On Thu, Feb 05, 2015 at 03:12:20AM +0100, Sedat Dilek wrote:
> On Thu, Feb 5, 2015 at 2:53 AM, Sedat Dilek <sedat.dilek@...il.com> wrote:
> > On Thu, Feb 5, 2015 at 2:51 AM, Paul E. McKenney
> > <paulmck@...ux.vnet.ibm.com> wrote:
> >> 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
> >>> <paulmck@...ux.vnet.ibm.com> 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
> >>> >> <paulmck@...ux.vnet.ibm.com> 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 :-)
> >>> >
> >>> > 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 <sedat.dilek@...il.com>
> >>> >> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> >>> >> >
> >>> >> > 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!
> >
> > Will you send a separate patch?
> >
> 
> Thanks, it's in rcu-next.
> 
> commit 33a741a1ea39f1daa821259c3654f5abf91d1690
> "x86/mm: Omit switch_mm() tracing for offline CPUs"
> 
> - Sedat -
> 
> [1] http://git.kernel.org/cgit/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=rcu/next&id=33a741a1ea39f1daa821259c3654f5abf91d1690

That is the one, but here it is as a patch as well.

							Thanx, Paul

------------------------------------------------------------------------

x86/mm: 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.

Fixes: d17d8f9dedb9 ("x86/mm: Add tracepoints for TLB flushes")
Reported-by: Sedat Dilek <sedat.dilek@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>

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);
 		}
 	}

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