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    SubjectRe: [PATCH tip/core/rcu 01/45] rcutorture: Add forward-progress checking for writer
    On Wed, May 07, 2014 at 02:16:49PM -0700, josh@joshtriplett.org wrote:
    > On Mon, Apr 28, 2014 at 05:24:49PM -0700, Paul E. McKenney wrote:
    > > From: "Paul E. McKenney" <paulmck@linux.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@linux.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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