[tip: core/rcu] rcu-tasks: Make rcutorture writer stall output include GP state

From: tip-bot2 for Paul E. McKenney
Date: Mon May 11 2020 - 16:59:57 EST

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The following commit has been merged into the core/rcu branch of tip:

Commit-ID: af051ca4e4231fcf5f366e28453ac28208bb36c6
Gitweb: https://git.kernel.org/tip/af051ca4e4231fcf5f366e28453ac28208bb36c6
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate: Mon, 16 Mar 2020 12:13:33 -07:00
Committer: Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 27 Apr 2020 11:03:52 -07:00

rcu-tasks: Make rcutorture writer stall output include GP state

This commit adds grace-period state and time to the rcutorture writer
stall output.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
kernel/rcu/tasks.h | 77 ++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 72 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index e4f8942..c93fb29 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -17,7 +17,7 @@ typedef void (*pregp_func_t)(void);
typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop);
typedef void (*postscan_func_t)(void);
typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp);
-typedef void (*postgp_func_t)(void);
+typedef void (*postgp_func_t)(struct rcu_tasks *rtp);

/**
* Definition for a Tasks-RCU-like mechanism.
@@ -27,6 +27,9 @@ typedef void (*postgp_func_t)(void);
* @cbs_lock: Lock protecting callback list.
* @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
* @gp_func: This flavor's grace-period-wait function.
+ * @gp_state: Grace period's most recent state transition (debugging).
+ * @gp_jiffies: Time of last @gp_state transition.
+ * @gp_start: Most recent grace-period start in jiffies.
* @pregp_func: This flavor's pre-grace-period function (optional).
* @pertask_func: This flavor's per-task scan function (optional).
* @postscan_func: This flavor's post-task scan function (optional).
@@ -41,6 +44,8 @@ struct rcu_tasks {
struct rcu_head **cbs_tail;
struct wait_queue_head cbs_wq;
raw_spinlock_t cbs_lock;
+ int gp_state;
+ unsigned long gp_jiffies;
struct task_struct *kthread_ptr;
rcu_tasks_gp_func_t gp_func;
pregp_func_t pregp_func;
@@ -73,10 +78,56 @@ DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
module_param(rcu_task_stall_timeout, int, 0644);

+/* RCU tasks grace-period state for debugging. */
+#define RTGS_INIT 0
+#define RTGS_WAIT_WAIT_CBS 1
+#define RTGS_WAIT_GP 2
+#define RTGS_PRE_WAIT_GP 3
+#define RTGS_SCAN_TASKLIST 4
+#define RTGS_POST_SCAN_TASKLIST 5
+#define RTGS_WAIT_SCAN_HOLDOUTS 6
+#define RTGS_SCAN_HOLDOUTS 7
+#define RTGS_POST_GP 8
+#define RTGS_WAIT_READERS 9
+#define RTGS_INVOKE_CBS 10
+#define RTGS_WAIT_CBS 11
+static const char * const rcu_tasks_gp_state_names[] = {
+ "RTGS_INIT",
+ "RTGS_WAIT_WAIT_CBS",
+ "RTGS_WAIT_GP",
+ "RTGS_PRE_WAIT_GP",
+ "RTGS_SCAN_TASKLIST",
+ "RTGS_POST_SCAN_TASKLIST",
+ "RTGS_WAIT_SCAN_HOLDOUTS",
+ "RTGS_SCAN_HOLDOUTS",
+ "RTGS_POST_GP",
+ "RTGS_WAIT_READERS",
+ "RTGS_INVOKE_CBS",
+ "RTGS_WAIT_CBS",
+};
+
////////////////////////////////////////////////////////////////////////
//
// Generic code.

+/* Record grace-period phase and time. */
+static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate)
+{
+ rtp->gp_state = newstate;
+ rtp->gp_jiffies = jiffies;
+}
+
+/* Return state name. */
+static const char *tasks_gp_state_getname(struct rcu_tasks *rtp)
+{
+ int i = data_race(rtp->gp_state); // Let KCSAN detect update races
+ int j = READ_ONCE(i); // Prevent the compiler from reading twice
+
+ if (j >= ARRAY_SIZE(rcu_tasks_gp_state_names))
+ return "???";
+ return rcu_tasks_gp_state_names[j];
+}
+
// Enqueue a callback for the specified flavor of Tasks RCU.
static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
struct rcu_tasks *rtp)
@@ -141,15 +192,18 @@ static int __noreturn rcu_tasks_kthread(void *arg)
READ_ONCE(rtp->cbs_head));
if (!rtp->cbs_head) {
WARN_ON(signal_pending(current));
+ set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS);
schedule_timeout_interruptible(HZ/10);
}
continue;
}

// Wait for one grace period.
+ set_tasks_gp_state(rtp, RTGS_WAIT_GP);
rtp->gp_func(rtp);

/* Invoke the callbacks. */
+ set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);
while (list) {
next = list->next;
local_bh_disable();
@@ -160,6 +214,8 @@ static int __noreturn rcu_tasks_kthread(void *arg)
}
/* Paranoid sleep to keep this from entering a tight loop */
schedule_timeout_uninterruptible(HZ/10);
+
+ set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
}
}

@@ -222,8 +278,11 @@ static void __init rcu_tasks_bootup_oddness(void)
/* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */
static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
{
- pr_info("%s %c%c %s\n",
+ pr_info("%s: %s(%d) since %lu %c%c %s\n",
rtp->kname,
+ tasks_gp_state_getname(rtp),
+ data_race(rtp->gp_state),
+ jiffies - data_race(rtp->gp_jiffies),
".k"[!!data_race(rtp->kthread_ptr)],
".C"[!!data_race(rtp->cbs_head)],
s);
@@ -243,6 +302,7 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
LIST_HEAD(holdouts);
int fract;

+ set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP);
rtp->pregp_func();

/*
@@ -251,11 +311,13 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
* that are not already voluntarily blocked. Mark these tasks
* and make a list of them in holdouts.
*/
+ set_tasks_gp_state(rtp, RTGS_SCAN_TASKLIST);
rcu_read_lock();
for_each_process_thread(g, t)
rtp->pertask_func(t, &holdouts);
rcu_read_unlock();

+ set_tasks_gp_state(rtp, RTGS_POST_SCAN_TASKLIST);
rtp->postscan_func();

/*
@@ -277,6 +339,7 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
break;

/* Slowly back off waiting for holdouts */
+ set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS);
schedule_timeout_interruptible(HZ/fract);

if (fract > 1)
@@ -288,10 +351,12 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
lastreport = jiffies;
firstreport = true;
WARN_ON(signal_pending(current));
+ set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS);
rtp->holdouts_func(&holdouts, needreport, &firstreport);
}

- rtp->postgp_func();
+ set_tasks_gp_state(rtp, RTGS_POST_GP);
+ rtp->postgp_func(rtp);
}

////////////////////////////////////////////////////////////////////////
@@ -394,7 +459,7 @@ static void check_all_holdout_tasks(struct list_head *hop,
}

/* Finish off the Tasks-RCU grace period. */
-static void rcu_tasks_postgp(void)
+static void rcu_tasks_postgp(struct rcu_tasks *rtp)
{
/*
* Because ->on_rq and ->nvcsw are not guaranteed to have a full
@@ -881,7 +946,7 @@ static void check_all_holdout_tasks_trace(struct list_head *hop,
}

/* Wait for grace period to complete and provide ordering. */
-static void rcu_tasks_trace_postgp(void)
+static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp)
{
bool firstreport;
struct task_struct *g, *t;
@@ -894,6 +959,7 @@ static void rcu_tasks_trace_postgp(void)
smp_mb__after_atomic(); // Order vs. later atomics

// Wait for readers.
+ set_tasks_gp_state(rtp, RTGS_WAIT_READERS);
for (;;) {
ret = wait_event_idle_exclusive_timeout(
trc_wait,
@@ -901,6 +967,7 @@ static void rcu_tasks_trace_postgp(void)
READ_ONCE(rcu_task_stall_timeout));
if (ret)
break; // Count reached zero.
+ // Stall warning time, so make a list of the offenders.
for_each_process_thread(g, t)
if (READ_ONCE(t->trc_reader_need_end))
trc_add_holdout(t, &holdouts);

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