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Date: Tue, 12 Jun 2012 07:47:05 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Sasha Levin <levinsasha928@...il.com>, Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <peterz@...radead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Dave Jones <davej@...hat.com>
Subject: Re: rcu,sched: spinlock recursion on 3.5-rc2
On Tue, Jun 12, 2012 at 03:40:13PM +0200, Thomas Gleixner wrote:
> On Tue, 12 Jun 2012, Sasha Levin wrote:
>
> > Hey all,
> >
> > I've got the following splat while fuzzing with trinity in a KVM tools guest on 3.5-rc2:
> >
> > [ 8110.274070] BUG: spinlock recursion on CPU#0, rcu_torture_rea/2658
> > [ 8110.275014] lock: 0xffff88000d9d6140, .magic: dead4ead, .owner: rcu_torture_rea/2658, .owner_cpu: 0
> > [ 8110.275014] Pid: 2658, comm: rcu_torture_rea Tainted: G W 3.5.0-rc2-sasha-00019-gbd68491 #376
> > [ 8110.275014] Call Trace:
> > [ 8110.275014] [<ffffffff8197de38>] spin_dump+0x78/0xc0
> > [ 8110.275014] [<ffffffff8197deab>] spin_bug+0x2b/0x40
> > [ 8110.275014] [<ffffffff8197dfee>] do_raw_spin_lock+0x4e/0x140
> > [ 8110.275014] [<ffffffff837c0b2b>] _raw_spin_lock+0x5b/0x70
> > [ 8110.275014] [<ffffffff8111d051>] ? rt_mutex_setprio+0x81/0x2c0
> > [ 8110.275014] [<ffffffff8111d051>] rt_mutex_setprio+0x81/0x2c0
> > [ 8110.275014] [<ffffffff81155160>] __rt_mutex_adjust_prio+0x20/0x30
> > [ 8110.275014] [<ffffffff837c0164>] rt_mutex_slowunlock+0x104/0x130
> > [ 8110.275014] [<ffffffff837c0199>] rt_mutex_unlock+0x9/0x10
> > [ 8110.275014] [<ffffffff81193e30>] rcu_read_unlock_special+0x350/0x400
> > [ 8110.275014] [<ffffffff8114841a>] ? get_lock_stats+0x2a/0x60
> > [ 8110.275014] [<ffffffff811941aa>] rcu_preempt_note_context_switch+0x22a/0x300
> > [ 8110.275014] [<ffffffff837bf8ca>] __schedule+0x76a/0x880
> > [ 8110.275014] [<ffffffff837c1c74>] ? retint_restore_args+0x13/0x13
> > [ 8110.275014] [<ffffffff8118dc20>] ? rcu_torture_read_unlock+0x40/0x60
> > [ 8110.275014] [<ffffffff837bff64>] preempt_schedule_irq+0x94/0xd0
> > [ 8110.275014] [<ffffffff837c1da6>] retint_kernel+0x26/0x30
> > [ 8110.275014] [<ffffffff81193ae1>] ? rcu_read_unlock_special+0x1/0x400
> > [ 8110.275014] [<ffffffff81193f2d>] ? __rcu_read_unlock+0x4d/0xa0
> > [ 8110.275014] [<ffffffff8118dc3d>] rcu_torture_read_unlock+0x5d/0x60
> > [ 8110.275014] [<ffffffff8118dedd>] rcu_torture_reader+0x29d/0x380
> > [ 8110.275014] [<ffffffff8118ca50>] ? T.865+0x50/0x50
> > [ 8110.275014] [<ffffffff8118dc40>] ? rcu_torture_read_unlock+0x60/0x60
> > [ 8110.275014] [<ffffffff81106e32>] kthread+0xb2/0xc0
> > [ 8110.275014] [<ffffffff837c39f4>] kernel_thread_helper+0x4/0x10
> > [ 8110.275014] [<ffffffff837c1c74>] ? retint_restore_args+0x13/0x13
> > [ 8110.275014] [<ffffffff81106d80>] ? __init_kthread_worker+0x70/0x70
> > [ 8110.275014] [<ffffffff837c39f0>] ? gs_change+0x13/0x13
>
> Ok, that's nasty.
>
> The torture thread got preempted. rcu_preempt_note_context_switch()
> tries to unlock the boosting rt mutex.
>
> Though rcu_preempt_note_context_switch() is called with rq lock
> held. So it's not a surprise that the code will dead lock.
>
> My brain hurts already from looking, so Paul to the rescue!
My brain hurts from beating my head on my desk. It seems that attempts
to enhance PREEMPT_RCU's read-side performance require even more paranoia
than I normally bring to bear. :-/
Please see below for what I expect is the relevant revert.
Thanx, Paul
------------------------------------------------------------------------
Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation"
This reverts commit 616c310e83b872024271c915c1b9ab505b9efad9
(Move PREEMPT_RCU preemption to switch_to() invocation) which can
result in runqueue deadlock.
Reported-by: Sasha Levin <levinsasha928@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index 88e466b..43b39d6 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -705,7 +705,6 @@ static void stack_proc(void *arg)
struct task_struct *from = current, *to = arg;
to->thread.saved_task = from;
- rcu_switch_from(from);
switch_to(from, to, from);
}
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 26d1a47..9cac722 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -184,7 +184,6 @@ static inline int rcu_preempt_depth(void)
/* Internal to kernel */
extern void rcu_sched_qs(int cpu);
extern void rcu_bh_qs(int cpu);
-extern void rcu_preempt_note_context_switch(void);
extern void rcu_check_callbacks(int cpu, int user);
struct notifier_block;
extern void rcu_idle_enter(void);
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index adb5e5a..148c6db 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -87,6 +87,10 @@ static inline void kfree_call_rcu(struct rcu_head *head,
#ifdef CONFIG_TINY_RCU
+static inline void rcu_preempt_note_context_switch(void)
+{
+}
+
static inline int rcu_needs_cpu(int cpu)
{
return 0;
@@ -94,6 +98,7 @@ static inline int rcu_needs_cpu(int cpu)
#else /* #ifdef CONFIG_TINY_RCU */
+void rcu_preempt_note_context_switch(void);
int rcu_preempt_needs_cpu(void);
static inline int rcu_needs_cpu(int cpu)
@@ -106,6 +111,7 @@ static inline int rcu_needs_cpu(int cpu)
static inline void rcu_note_context_switch(int cpu)
{
rcu_sched_qs(cpu);
+ rcu_preempt_note_context_switch();
}
/*
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4059c0f..06a4c5f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1871,22 +1871,12 @@ static inline void rcu_copy_process(struct task_struct *p)
INIT_LIST_HEAD(&p->rcu_node_entry);
}
-static inline void rcu_switch_from(struct task_struct *prev)
-{
- if (prev->rcu_read_lock_nesting != 0)
- rcu_preempt_note_context_switch();
-}
-
#else
static inline void rcu_copy_process(struct task_struct *p)
{
}
-static inline void rcu_switch_from(struct task_struct *prev)
-{
-}
-
#endif
#ifdef CONFIG_SMP
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0da7b88..d994530 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -201,6 +201,7 @@ void rcu_note_context_switch(int cpu)
{
trace_rcu_utilization("Start context switch");
rcu_sched_qs(cpu);
+ rcu_preempt_note_context_switch(cpu);
trace_rcu_utilization("End context switch");
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 7f5d138..bd220db 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -430,6 +430,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work);
/* Forward declarations for rcutree_plugin.h */
static void rcu_bootup_announce(void);
long rcu_batches_completed(void);
+static void rcu_preempt_note_context_switch(int cpu);
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 2411000..fb6e07e 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -153,7 +153,7 @@ static void rcu_preempt_qs(int cpu)
*
* Caller must disable preemption.
*/
-void rcu_preempt_note_context_switch(void)
+static void rcu_preempt_note_context_switch(int cpu)
{
struct task_struct *t = current;
unsigned long flags;
@@ -164,7 +164,7 @@ void rcu_preempt_note_context_switch(void)
(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
/* Possibly blocking in an RCU read-side critical section. */
- rdp = __this_cpu_ptr(rcu_preempt_state.rda);
+ rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave(&rnp->lock, flags);
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
@@ -228,7 +228,7 @@ void rcu_preempt_note_context_switch(void)
* means that we continue to block the current grace period.
*/
local_irq_save(flags);
- rcu_preempt_qs(smp_processor_id());
+ rcu_preempt_qs(cpu);
local_irq_restore(flags);
}
@@ -1002,6 +1002,14 @@ void rcu_force_quiescent_state(void)
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * CPUs being in quiescent states.
+ */
+static void rcu_preempt_note_context_switch(int cpu)
+{
+}
+
+/*
* Because preemptible RCU does not exist, there are never any preempted
* RCU readers.
*/
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d5594a4..eaead2d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2081,7 +2081,6 @@ context_switch(struct rq *rq, struct task_struct *prev,
#endif
/* Here we just switch the register state and the stack. */
- rcu_switch_from(prev);
switch_to(prev, next, prev);
barrier();
--
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