Message-ID: <20120403145839.GB2302@linux.vnet.ibm.com>
Date:	Tue, 3 Apr 2012 07:58:39 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Catalin Marinas <catalin.marinas@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: kmemleak: illegal RCU use assertion error

On Tue, Apr 03, 2012 at 02:10:43AM +0300, Sergey Senozhatsky wrote:
> On (04/02/12 06:09), Paul E. McKenney wrote:
> > On Mon, Apr 02, 2012 at 10:09:11AM +0300, Sergey Senozhatsky wrote:
> > > Hello,
> > > 
> > > commit e5601400081651060a59bd1f45f2821bb8e97f95
> > > Author: Paul E. McKenney <paul.mckenney@...aro.org>
> > > Date:   Sat Jan 7 11:03:57 2012 -0800
> > > 
> > >     rcu: Simplify offline processing
> > >     
> > >     Move ->qsmaskinit and blkd_tasks[] manipulation to the CPU_DYING
> > >     notifier.  This simplifies the code by eliminating a potential
> > >     deadlock and by reducing the responsibilities of force_quiescent_state().
> > >     Also rename functions to make their connection to the CPU-hotplug
> > >     stages explicit.
> > >     
> > >     Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> > >     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > 
> > > 
> > > introduced WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); to __call_rcu()
> > > function, Paul also added cpu_offline checks to other routines (e.g. callbacks)
> > > in later commits. It happens that kmemleak() triggers one of them.
> > > 
> > > During cpu core offline, kfree()->kmemleak_free()->put_object()-->__call_rcu() chain
> > > for struct intel_shared_regs * is executed when no struct users left on this core -- 
> > > all CPUs are dead or dying.
> > > 
> > > 
> > > [ 4703.342462] CPU 3 is now offline
> > > [ 4705.588116] ------------[ cut here ]------------
> > > [ 4705.588129] WARNING: at kernel/rcutree.c:1823 __call_rcu+0x9d/0x1d2()
> > > [..]
> > > [ 4705.588196] Call Trace:
> > > [ 4705.588207]  [<ffffffff81059a00>] ? synchronize_srcu+0x6/0x17
> > > [ 4705.588215]  [<ffffffff8103364e>] warn_slowpath_common+0x83/0x9c
> > > [ 4705.588223]  [<ffffffff8111e627>] ? get_object+0x31/0x31
> > > [ 4705.588229]  [<ffffffff81033681>] warn_slowpath_null+0x1a/0x1c
> > > [ 4705.588235]  [<ffffffff810af770>] __call_rcu+0x9d/0x1d2
> > > [ 4705.588243]  [<ffffffff81013f52>] ? intel_pmu_cpu_dying+0x3b/0x5d
> > > [ 4705.588249]  [<ffffffff810af8f1>] call_rcu_sched+0x17/0x19
> > > [ 4705.588255]  [<ffffffff8111eb7e>] put_object+0x47/0x4b
> > > [ 4705.588261]  [<ffffffff8111ed8b>] delete_object_full+0x2a/0x2e
> > > [ 4705.588269]  [<ffffffff81491dc8>] kmemleak_free+0x26/0x45
> > > [ 4705.588274]  [<ffffffff8111691f>] kfree+0x130/0x221
> > > [ 4705.588280]  [<ffffffff81013f52>] intel_pmu_cpu_dying+0x3b/0x5d
> > > [ 4705.588287]  [<ffffffff8149cb83>] x86_pmu_notifier+0xaf/0xb9
> > > [ 4705.588296]  [<ffffffff814b0e9d>] notifier_call_chain+0xac/0xd9
> > > [ 4705.588303]  [<ffffffff81059c9e>] __raw_notifier_call_chain+0xe/0x10
> > > [ 4705.588309]  [<ffffffff810354ec>] __cpu_notify+0x20/0x37
> > > [ 4705.588314]  [<ffffffff81035516>] cpu_notify+0x13/0x15
> > > [ 4705.588320]  [<ffffffff81490fab>] take_cpu_down+0x28/0x2e
> > > [ 4705.588326]  [<ffffffff8109ef7f>] stop_machine_cpu_stop+0x96/0xf1
> > > [ 4705.588332]  [<ffffffff8109ece3>] cpu_stopper_thread+0xe3/0x183
> > > [ 4705.588338]  [<ffffffff8109eee9>] ? queue_stop_cpus_work+0xd0/0xd0
> > > [ 4705.588344]  [<ffffffff814ad382>] ? _raw_spin_unlock_irqrestore+0x47/0x65
> > > [ 4705.588353]  [<ffffffff81087d0d>] ? trace_hardirqs_on_caller+0x119/0x175
> > > [ 4705.588358]  [<ffffffff81087d76>] ? trace_hardirqs_on+0xd/0xf
> > > [ 4705.588364]  [<ffffffff8109ec00>] ? cpu_stop_signal_done+0x2c/0x2c
> > > [ 4705.588370]  [<ffffffff810544a9>] kthread+0x8b/0x93
> > > [ 4705.588378]  [<ffffffff814b5f34>] kernel_thread_helper+0x4/0x10
> > > [ 4705.588385]  [<ffffffff814ad7f0>] ? retint_restore_args+0x13/0x13
> > > [ 4705.588391]  [<ffffffff8105441e>] ? __init_kthread_worker+0x5a/0x5a
> > > [ 4705.588397]  [<ffffffff814b5f30>] ? gs_change+0x13/0x13
> > > [ 4705.588400] ---[ end trace 720328982e35a713 ]---
> > > [ 4705.588507] CPU 2 is now offline
> > > 
> > > 
> > > My first solution was to return from delete_object() if object deallocation
> > > performed on cpu_is_offline(smp_processor_id()), marking object with special
> > > flag, say OBJECT_ORPHAN. And issue real object_delete() during scan (for example)
> > > when we see OBJECT_ORPHAN object.  
> > > That, however, requires to handle special case when cpu core offlined
> > > for small period of time, leading to object insertion error in
> > > create_object(), which either may be handled in 2 possible ways (assuming
> > > that lookup_object() returned OBJECT_ORPHAN):
> > > #1 delete orphaned object and retry with insertion (*)
> > > #2 re-set existing orphan object
> > > 
> > > 
> > > (*) performing delete_object() from within create_object() requires releasing
> > > of held kmemleak and object locks, which is racy with other create_object() and
> > > any possible scan() activities.
> > > 
> > > Yet I'm not exactly sure that option #2 is the correct one.
> > > (I've kind of a patch [not properly tested, etc.] for #2 option).
> > 
> > Alternatively, I can make RCU tolerate __call_rcu() from late in the
> > CPU_DYING notifiers without too much trouble.
> > 
> 
> Well, if that will `do the trick', then I'm ready to test it.

If you are feeling lucky, please try out the attached untested patch.
I will repost in the rather likely event that my testing finds bugs.

							Thanx, Paul

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

 rcutree.c |   31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

rcu: Permit call_rcu() from CPU_DYING notifiers

As of commit 29494be7, RCU adopts callbacks from the dying CPU in
its CPU_DYING notifier, which means that any callbacks posted by
later CPU_DYING notifiers are ignored until the CPU comes back
online.  A WARN_ON_ONCE() was added to __call_rcu() by commit
e5601400 to check for this condition, which recently triggered
(https://lkml.org/lkml/2012/4/2/34).

This commit therefore causes RCU's CPU_DEAD notifier to adopt any
callbacks that were posted by CPU_DYING notifiers and removes the
WARN_ON_ONCE() from __call_rcu().

Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 1050d6d..4c927e6 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1406,11 +1406,41 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 {
 	unsigned long flags;
+	int i;
 	unsigned long mask;
 	int need_report = 0;
 	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
 	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rnp. */
 
+	/* If a CPU_DYING notifier has enqueued callbacks, adopt them. */
+	if (rdp->nxtlist != NULL) {
+		struct rcu_data *receive_rdp;
+
+		local_irq_save(flags);
+		receive_rdp = per_cpu_ptr(rsp->rda, smp_processor_id());
+
+		/* Adjust the counts. */
+		receive_rdp->qlen_lazy += rdp->qlen_lazy;
+		receive_rdp->qlen += rdp->qlen;
+		rdp->qlen_lazy = 0;
+		rdp->qlen = 0;
+
+		/*
+		 * Adopt all callbacks.  The outgoing CPU was in no shape
+		 * to advance them, so make them all go through a full
+		 * grace period.
+		 */
+		*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
+		receive_rdp->nxttail[RCU_NEXT_TAIL] =
+			rdp->nxttail[RCU_NEXT_TAIL];
+		local_irq_restore(flags);
+
+		/* Initialize the outgoing CPU's callback list. */
+		rdp->nxtlist = NULL;
+		for (i = 0; i < RCU_NEXT_SIZE; i++)
+			rdp->nxttail[i] = &rdp->nxtlist;
+	}
+
 	/* Adjust any no-longer-needed kthreads. */
 	rcu_stop_cpu_kthread(cpu);
 	rcu_node_kthread_setaffinity(rnp, -1);
@@ -1820,7 +1850,6 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
 	 * a quiescent state betweentimes.
 	 */
 	local_irq_save(flags);
-	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
 	rdp = this_cpu_ptr(rsp->rda);
 
 	/* Add the callback to our list. */

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