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Message-ID: <20130821030324.GQ29406@linux.vnet.ibm.com>
Date: Tue, 20 Aug 2013 20:03:24 -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 Wed, Aug 21, 2013 at 10:40:15AM +0800, Lai Jiangshan wrote:
> 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();
Fair point, no chance of the second rh2 callback being queued after the
first one is invoked! I will leave the message. Whoever sees it with
the current code will have something to tell their grandchildren.
Thanx, Paul
> > 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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>
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