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Date: Wed, 21 Aug 2013 10:40:15 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: paulmck@...ux.vnet.ibm.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 08/21/2013 02:38 AM, Paul E. McKenney wrote:
> 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...
I still don't understand why rcu_torture_err_cb() will be called when:
rcu_read_lock();
call_rcu(&rh2, rcu_torture_leak_cb);
call_rcu(&rh2, rcu_torture_err_cb); // rh2 will be still queued here,
// debug-objects will find it and
// change it to rcu_leak_callback()
rcu_read_unlock();
>
> 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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