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Date: Tue, 20 Aug 2013 11:38:43 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Lai Jiangshan <laijs@...fujitsu.com>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
sbw@....edu, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Sedat Dilek <sedat.dilek@...il.com>,
Davidlohr Bueso <davidlohr.bueso@...com>,
Rik van Riel <riel@...riel.com>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH tip/core/rcu 1/5] rcu: Add duplicate-callback tests to
rcutorture
On Tue, Aug 20, 2013 at 06:02:39PM +0800, Lai Jiangshan wrote:
> On 08/20/2013 10:51 AM, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> >
> > This commit adds a object_debug option to rcutorture to allow the
> > debug-object-based checks for duplicate call_rcu() invocations to
> > be deterministically tested.
> >
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Sedat Dilek <sedat.dilek@...il.com>
> > Cc: Davidlohr Bueso <davidlohr.bueso@...com>
> > Cc: Rik van Riel <riel@...riel.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> > [ paulmck: Banish mid-function ifdef, more or less per Josh Triplett. ]
> > ---
> > kernel/rcutorture.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 45 insertions(+)
> >
> > diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
> > index 3d936f0f..f5cf2bb 100644
> > --- a/kernel/rcutorture.c
> > +++ b/kernel/rcutorture.c
> > @@ -66,6 +66,7 @@ static int fqs_duration; /* Duration of bursts (us), 0 to disable. */
> > static int fqs_holdoff; /* Hold time within burst (us). */
> > static int fqs_stutter = 3; /* Wait time between bursts (s). */
> > static int n_barrier_cbs; /* Number of callbacks to test RCU barriers. */
> > +static int object_debug; /* Test object-debug double call_rcu()?. */
> > static int onoff_interval; /* Wait time between CPU hotplugs, 0=disable. */
> > static int onoff_holdoff; /* Seconds after boot before CPU hotplugs. */
> > static int shutdown_secs; /* Shutdown time (s). <=0 for no shutdown. */
> > @@ -100,6 +101,8 @@ module_param(fqs_stutter, int, 0444);
> > MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
> > module_param(n_barrier_cbs, int, 0444);
> > MODULE_PARM_DESC(n_barrier_cbs, "# of callbacks/kthreads for barrier testing");
> > +module_param(object_debug, int, 0444);
> > +MODULE_PARM_DESC(object_debug, "Enable debug-object double call_rcu() testing");
> > module_param(onoff_interval, int, 0444);
> > MODULE_PARM_DESC(onoff_interval, "Time between CPU hotplugs (s), 0=disable");
> > module_param(onoff_holdoff, int, 0444);
> > @@ -1934,6 +1937,46 @@ rcu_torture_cleanup(void)
> > rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
> > }
> >
> > +#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
> > +static void rcu_torture_leak_cb(struct rcu_head *rhp)
> > +{
> > +}
> > +
> > +static void rcu_torture_err_cb(struct rcu_head *rhp)
> > +{
> > + /* This -might- happen due to race conditions, but is unlikely. */
> > + pr_alert("rcutorture: duplicated callback was invoked.\n");
> > +}
> > +#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
> > +
> > +/*
> > + * Verify that double-free causes debug-objects to complain, but only
> > + * if CONFIG_DEBUG_OBJECTS_RCU_HEAD=y. Otherwise, say that the test
> > + * cannot be carried out.
> > + */
> > +static void rcu_test_debug_objects(void)
> > +{
> > +#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
> > + struct rcu_head rh1;
> > + struct rcu_head rh2;
> > +
> > + init_rcu_head_on_stack(&rh1);
> > + init_rcu_head_on_stack(&rh2);
> > + pr_alert("rcutorture: WARN: Duplicate call_rcu() test starting.\n");
> > + local_irq_disable(); /* Make it hard to finish grace period. */
>
> you can use rcu_read_lock() directly.
I could do that as well, but it doesn't do everything that local_irq_disable()
does.
Right, which means that my comment is bad. Fixing both, thank you!
> > + call_rcu(&rh1, rcu_torture_leak_cb); /* start grace period. */
And the one above cannot start a grace period due to irqs being enabled.
Which is -almost- always OK, but...
> > + call_rcu(&rh2, rcu_torture_err_cb);
And this one should invoke rcu_torture_leak_cb instead of
rcu_torture_err_cb(). Just results in a confusing error message, but...
OK, a few more fixes, then!
> > + call_rcu(&rh2, rcu_torture_err_cb); /* duplicate callback. */
> > + local_irq_enable();
> > + rcu_barrier();
> > + pr_alert("rcutorture: WARN: Duplicate call_rcu() test complete.\n");
> > + destroy_rcu_head_on_stack(&rh1);
> > + destroy_rcu_head_on_stack(&rh2);
> > +#else /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
> > + pr_alert("rcutorture: !CONFIG_DEBUG_OBJECTS_RCU_HEAD, not testing duplicate call_rcu()\n");
> > +#endif /* #else #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
> > +}
The result is as follows. Better?
Thanx, Paul
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
static void rcu_torture_leak_cb(struct rcu_head *rhp)
{
}
static void rcu_torture_err_cb(struct rcu_head *rhp)
{
/*
* This -might- happen due to race conditions, but is unlikely.
* The scenario that leads to this happening is that the
* first of the pair of duplicate callbacks is queued,
* someone else starts a grace period that includes that
* callback, then the second of the pair must wait for the
* next grace period. Unlikely, but can happen. If it
* does happen, the debug-objects subsystem won't have splatted.
*/
pr_alert("rcutorture: duplicated callback was invoked.\n");
}
#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
/*
* Verify that double-free causes debug-objects to complain, but only
* if CONFIG_DEBUG_OBJECTS_RCU_HEAD=y. Otherwise, say that the test
* cannot be carried out.
*/
static void rcu_test_debug_objects(void)
{
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
struct rcu_head rh1;
struct rcu_head rh2;
init_rcu_head_on_stack(&rh1);
init_rcu_head_on_stack(&rh2);
pr_alert("rcutorture: WARN: Duplicate call_rcu() test starting.\n");
preempt_disable(); /* Prevent preemption from interrupting test. */
rcu_read_lock(); /* Make it impossible to finish a grace period. */
call_rcu(&rh1, rcu_torture_leak_cb); /* Start grace period. */
local_irq_disable(); /* Make it harder to start a new grace period. */
call_rcu(&rh2, rcu_torture_leak_cb);
call_rcu(&rh2, rcu_torture_err_cb); /* Duplicate callback. */
local_irq_enable();
rcu_read_unlock();
preempt_enable();
rcu_barrier();
pr_alert("rcutorture: WARN: Duplicate call_rcu() test complete.\n");
destroy_rcu_head_on_stack(&rh1);
destroy_rcu_head_on_stack(&rh2);
#else /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
pr_alert("rcutorture: !CONFIG_DEBUG_OBJECTS_RCU_HEAD, not testing duplicate call_rcu()\n");
#endif /* #else #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
}
> > +
> > static int __init
> > rcu_torture_init(void)
> > {
> > @@ -2163,6 +2206,8 @@ rcu_torture_init(void)
> > firsterr = retval;
> > goto unwind;
> > }
> > + if (object_debug)
> > + rcu_test_debug_objects();
> > rcutorture_record_test_transition();
> > mutex_unlock(&fullstop_mutex);
> > return 0;
>
--
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