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Date: Wed, 7 May 2014 16:43:13 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: josh@...htriplett.org
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org,
laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
darren@...art.com, fweisbec@...il.com, oleg@...hat.com, sbw@....edu
Subject: Re: [PATCH tip/core/rcu 01/45] rcutorture: Add forward-progress
checking for writer
On Wed, May 07, 2014 at 02:16:49PM -0700, josh@...htriplett.org wrote:
> On Mon, Apr 28, 2014 at 05:24:49PM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> >
> > The rcutorture output currently does not distinguish between stalls in
> > the RCU implementation and stalls in the rcu_torture_writer() kthreads.
> > This commit therefore adds some diagnostics to help distinguish between
> > these two conditions, at least for the non-SRCU implementations. (SRCU
> > does not provide evidence of update-side forward progress by design.)
> >
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>
> The concept makes sense, and the writer state annotations seem like a
> useful debugging mechanism, but having RCU know about RCU torture types
> seems fundamentally wrong. This mechanism accesses rcu_state, which is
> already implementation-specific, so why not just only define the
> function for the RCU implementations that support it, and then have a
> function pointer in the torture-test structure to report a stall?
Ouch. It is worse than that! When running RCU-bh or RCU-sched,
the current code incorrectly returns the statistics for RCU.
So I do need some way for rcutorture to tell RCU which flavor
it is testing.
One thing I could do would be to pass in a pointer to the call_rcu()
function (cur_ops->call from rcutorture's viewpoint), then scan the
rcu_state structures looking for the selected flavor (rsp->call from
tree.c's viewpoint). In the SRCU and RCU-busted cases, the flavor would
not be found, and I could then just set everything to zero.
Does that seem reasonable, or is there a better way to do this?
Thanx, Paul
> - Josh Triplett
>
> > include/linux/rcupdate.h | 19 +++++++++++++++++++
> > kernel/rcu/rcutorture.c | 37 +++++++++++++++++++++++++++++++++++++
> > kernel/rcu/tree.c | 18 ++++++++++++++++++
> > 3 files changed, 74 insertions(+)
> >
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 00a7fd61b3c6..a6c3898e141e 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -51,7 +51,17 @@ extern int rcu_expedited; /* for sysctl */
> > extern int rcutorture_runnable; /* for sysctl */
> > #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
> >
> > +enum rcutorture_type {
> > + RTORT_BUSTED,
> > + RTORT_RCU,
> > + RTORT_RCU_BH,
> > + RTORT_RCU_SCHED,
> > + RTORT_SRCU
> > +};
> > +
> > #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
> > +void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
> > + unsigned long *gpnum, unsigned long *completed);
> > void rcutorture_record_test_transition(void);
> > void rcutorture_record_progress(unsigned long vernum);
> > void do_trace_rcu_torture_read(const char *rcutorturename,
> > @@ -60,6 +70,15 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
> > unsigned long c_old,
> > unsigned long c);
> > #else
> > +static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
> > + int *flags,
> > + unsigned long *gpnum,
> > + unsigned long *completed)
> > +{
> > + *flags = 0;
> > + *gpnum = 0;
> > + *completed = 0;
> > +}
> > static inline void rcutorture_record_test_transition(void)
> > {
> > }
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index bd30bc61bc05..1110db210318 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -138,6 +138,15 @@ static long n_barrier_attempts;
> > static long n_barrier_successes;
> > static struct list_head rcu_torture_removed;
> >
> > +static int rcu_torture_writer_state;
> > +#define RTWS_FIXED_DELAY 0
> > +#define RTWS_DELAY 1
> > +#define RTWS_REPLACE 2
> > +#define RTWS_DEF_FREE 3
> > +#define RTWS_EXP_SYNC 4
> > +#define RTWS_STUTTER 5
> > +#define RTWS_STOPPING 6
> > +
> > #if defined(MODULE) || defined(CONFIG_RCU_TORTURE_TEST_RUNNABLE)
> > #define RCUTORTURE_RUNNABLE_INIT 1
> > #else
> > @@ -214,6 +223,7 @@ rcu_torture_free(struct rcu_torture *p)
> > */
> >
> > struct rcu_torture_ops {
> > + int ttype;
> > void (*init)(void);
> > int (*readlock)(void);
> > void (*read_delay)(struct torture_random_state *rrsp);
> > @@ -312,6 +322,7 @@ static void rcu_sync_torture_init(void)
> > }
> >
> > static struct rcu_torture_ops rcu_ops = {
> > + .ttype = RTORT_RCU,
> > .init = rcu_sync_torture_init,
> > .readlock = rcu_torture_read_lock,
> > .read_delay = rcu_read_delay,
> > @@ -355,6 +366,7 @@ static void rcu_bh_torture_deferred_free(struct rcu_torture *p)
> > }
> >
> > static struct rcu_torture_ops rcu_bh_ops = {
> > + .ttype = RTORT_RCU_BH,
> > .init = rcu_sync_torture_init,
> > .readlock = rcu_bh_torture_read_lock,
> > .read_delay = rcu_read_delay, /* just reuse rcu's version. */
> > @@ -397,6 +409,7 @@ call_rcu_busted(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
> > }
> >
> > static struct rcu_torture_ops rcu_busted_ops = {
> > + .ttype = RTORT_BUSTED,
> > .init = rcu_sync_torture_init,
> > .readlock = rcu_torture_read_lock,
> > .read_delay = rcu_read_delay, /* just reuse rcu's version. */
> > @@ -492,6 +505,7 @@ static void srcu_torture_synchronize_expedited(void)
> > }
> >
> > static struct rcu_torture_ops srcu_ops = {
> > + .ttype = RTORT_SRCU,
> > .init = rcu_sync_torture_init,
> > .readlock = srcu_torture_read_lock,
> > .read_delay = srcu_read_delay,
> > @@ -527,6 +541,7 @@ static void rcu_sched_torture_deferred_free(struct rcu_torture *p)
> > }
> >
> > static struct rcu_torture_ops sched_ops = {
> > + .ttype = RTORT_RCU_SCHED,
> > .init = rcu_sync_torture_init,
> > .readlock = sched_torture_read_lock,
> > .read_delay = rcu_read_delay, /* just reuse rcu's version. */
> > @@ -699,12 +714,15 @@ rcu_torture_writer(void *arg)
> > set_user_nice(current, MAX_NICE);
> >
> > do {
> > + rcu_torture_writer_state = RTWS_FIXED_DELAY;
> > schedule_timeout_uninterruptible(1);
> > rp = rcu_torture_alloc();
> > if (rp == NULL)
> > continue;
> > rp->rtort_pipe_count = 0;
> > + rcu_torture_writer_state = RTWS_DELAY;
> > udelay(torture_random(&rand) & 0x3ff);
> > + rcu_torture_writer_state = RTWS_REPLACE;
> > old_rp = rcu_dereference_check(rcu_torture_current,
> > current == writer_task);
> > rp->rtort_mbtest = 1;
> > @@ -721,8 +739,10 @@ rcu_torture_writer(void *arg)
> > else
> > exp = gp_exp;
> > if (!exp) {
> > + rcu_torture_writer_state = RTWS_DEF_FREE;
> > cur_ops->deferred_free(old_rp);
> > } else {
> > + rcu_torture_writer_state = RTWS_EXP_SYNC;
> > cur_ops->exp_sync();
> > list_add(&old_rp->rtort_free,
> > &rcu_torture_removed);
> > @@ -743,8 +763,10 @@ rcu_torture_writer(void *arg)
> > }
> > }
> > rcutorture_record_progress(++rcu_torture_current_version);
> > + rcu_torture_writer_state = RTWS_STUTTER;
> > stutter_wait("rcu_torture_writer");
> > } while (!torture_must_stop());
> > + rcu_torture_writer_state = RTWS_STOPPING;
> > torture_kthread_stopping("rcu_torture_writer");
> > return 0;
> > }
> > @@ -937,6 +959,7 @@ rcu_torture_printk(char *page)
> > int i;
> > long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
> > long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
> > + static unsigned long rtcv_snap = ULONG_MAX;
> >
> > for_each_possible_cpu(cpu) {
> > for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
> > @@ -997,6 +1020,20 @@ rcu_torture_printk(char *page)
> > page += sprintf(page, "\n");
> > if (cur_ops->stats)
> > cur_ops->stats(page);
> > + if (rtcv_snap == rcu_torture_current_version &&
> > + rcu_torture_current != NULL) {
> > + int __maybe_unused flags;
> > + unsigned long __maybe_unused gpnum;
> > + unsigned long __maybe_unused completed;
> > +
> > + rcutorture_get_gp_data(cur_ops->ttype,
> > + &flags, &gpnum, &completed);
> > + page += sprintf(page,
> > + "??? Writer stall state %d g%lu c%lu f%#x\n",
> > + rcu_torture_writer_state,
> > + gpnum, completed, flags);
> > + }
> > + rtcv_snap = rcu_torture_current_version;
> > }
> >
> > /*
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 0c47e300210a..032106df7391 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -294,6 +294,24 @@ void rcutorture_record_test_transition(void)
> > EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
> >
> > /*
> > + * Send along grace-period-related data for rcutorture diagnostics.
> > + */
> > +void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
> > + unsigned long *gpnum, unsigned long *completed)
> > +{
> > + if (test_type == RTORT_SRCU || test_type == RTORT_BUSTED) {
> > + *flags = 0;
> > + *gpnum = 0;
> > + *completed = 0;
> > + return;
> > + }
> > + *flags = ACCESS_ONCE(rcu_state->gp_flags);
> > + *gpnum = ACCESS_ONCE(rcu_state->gpnum);
> > + *completed = ACCESS_ONCE(rcu_state->completed);
> > +}
> > +EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
> > +
> > +/*
> > * Record the number of writer passes through the current rcutorture test.
> > * This is also used to correlate debugfs tracing stats with the rcutorture
> > * messages.
> > --
> > 1.8.1.5
> >
>
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