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Date: Wed, 7 May 2014 14:16:49 -0700
From: josh@...htriplett.org
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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 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?
- 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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