Commit-ID: c116dba68d19246639e4fdb8c75756c67d6d268f
Gitweb: https://git.kernel.org/tip/c116dba68d19246639e4fdb8c75756c67d6d268f
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Fri, 13 Jul 2018 12:09:14 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Thu, 30 Aug 2018 16:03:40 -0700
rcutorture: Dump reader protection sequence if failures or close calls
Now that RCU can have readers with multiple segments, it is quite
possible that a specific sequence of reader segments might result in
an rcutorture failure (reader spans a full grace period as detected
by one of the grace-period primitives) or an rcutorture close call
(reader potentially spans a full grace period based on reading out
the RCU implementation's grace-period counter, but with no ordering).
In such cases, it would clearly ease debugging if the offending specific
sequence was known. For the first reader encountering a failure or a
close call, this commit therefore dumps out the segments, delay durations,
and whether or not the reader was preempted.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
[ paulmck: Mark variables static, as suggested by kbuild test robot. ]
---
kernel/rcu/rcutorture.c | 119 ++++++++++++++++++++++++++++++++++++++----------
1 file changed, 96 insertions(+), 23 deletions(-)
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 294b3f6b7eb6..1141e0d84ff1 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -78,6 +78,7 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@xxxxxxxxxx> and Josh Triplett <josh@jos
RCUTORTURE_RDR_RBH | RCUTORTURE_RDR_SCHED)
#define RCUTORTURE_RDR_MAX_LOOPS 0x7 /* Maximum reader extensions. */
/* Must be power of two minus one. */
+#define RCUTORTURE_RDR_MAX_SEGS (RCUTORTURE_RDR_MAX_LOOPS + 3)
torture_param(int, cbflood_inter_holdoff, HZ,
"Holdoff between floods (jiffies)");
@@ -200,6 +201,18 @@ static const char * const rcu_torture_writer_state_names[] = {
"RTWS_STOPPING",
};
+/* Record reader segment types and duration for first failing read. */
+struct rt_read_seg {
+ int rt_readstate;
+ unsigned long rt_delay_jiffies;
+ unsigned long rt_delay_ms;
+ unsigned long rt_delay_us;
+ bool rt_preempted;
+};
+static int err_segs_recorded;
+static struct rt_read_seg err_segs[RCUTORTURE_RDR_MAX_SEGS];
+static int rt_read_nsegs;
+
static const char *rcu_torture_writer_state_getname(void)
{
unsigned int i = READ_ONCE(rcu_torture_writer_state);
@@ -281,7 +294,8 @@ struct rcu_torture_ops {
void (*init)(void);
void (*cleanup)(void);
int (*readlock)(void);
- void (*read_delay)(struct torture_random_state *rrsp);
+ void (*read_delay)(struct torture_random_state *rrsp,
+ struct rt_read_seg *rtrsp);
void (*readunlock)(int idx);
unsigned long (*get_gp_seq)(void);
unsigned long (*gp_diff)(unsigned long new, unsigned long old);
@@ -313,7 +327,8 @@ static int rcu_torture_read_lock(void) __acquires(RCU)
return 0;
}
-static void rcu_read_delay(struct torture_random_state *rrsp)
+static void
+rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
{
unsigned long started;
unsigned long completed;
@@ -329,15 +344,20 @@ static void rcu_read_delay(struct torture_random_state *rrsp)
started = cur_ops->get_gp_seq();
ts = rcu_trace_clock_local();
mdelay(longdelay_ms);
+ rtrsp->rt_delay_ms = longdelay_ms;
completed = cur_ops->get_gp_seq();
do_trace_rcu_torture_read(cur_ops->name, NULL, ts,
started, completed);
}
- if (!(torture_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
+ if (!(torture_random(rrsp) % (nrealreaders * 2 * shortdelay_us))) {
udelay(shortdelay_us);
+ rtrsp->rt_delay_us = shortdelay_us;
+ }
if (!preempt_count() &&
- !(torture_random(rrsp) % (nrealreaders * 500)))
+ !(torture_random(rrsp) % (nrealreaders * 500))) {
torture_preempt_schedule(); /* QS only if preemptible. */
+ rtrsp->rt_preempted = true;
+ }
}
static void rcu_torture_read_unlock(int idx) __releases(RCU)
@@ -494,7 +514,8 @@ static int srcu_torture_read_lock(void) __acquires(srcu_ctlp)
return srcu_read_lock(srcu_ctlp);
}
-static void srcu_read_delay(struct torture_random_state *rrsp)
+static void
+srcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
{
long delay;
const long uspertick = 1000000 / HZ;
@@ -504,10 +525,12 @@ static void srcu_read_delay(struct torture_random_state *rrsp)
delay = torture_random(rrsp) %
(nrealreaders * 2 * longdelay * uspertick);
- if (!delay && in_task())
+ if (!delay && in_task()) {
schedule_timeout_interruptible(longdelay);
- else
- rcu_read_delay(rrsp);
+ rtrsp->rt_delay_jiffies = longdelay;
+ } else {
+ rcu_read_delay(rrsp, rtrsp);
+ }
}
static void srcu_torture_read_unlock(int idx) __releases(srcu_ctlp)
@@ -1120,7 +1143,8 @@ static void rcu_torture_timer_cb(struct rcu_head *rhp)
* change, do a ->read_delay().
*/
static void rcutorture_one_extend(int *readstate, int newstate,
- struct torture_random_state *trsp)
+ struct torture_random_state *trsp,
+ struct rt_read_seg *rtrsp)
{
int idxnew = -1;
int idxold = *readstate;
@@ -1129,6 +1153,7 @@ static void rcutorture_one_extend(int *readstate, int newstate,
WARN_ON_ONCE(idxold < 0);
WARN_ON_ONCE((idxold >> RCUTORTURE_RDR_SHIFT) > 1);
+ rtrsp->rt_readstate = newstate;
/* First, put new protection in place to avoid critical-section gap. */
if (statesnew & RCUTORTURE_RDR_BH)
@@ -1160,7 +1185,7 @@ static void rcutorture_one_extend(int *readstate, int newstate,
/* Delay if neither beginning nor end and there was a change. */
if ((statesnew || statesold) && *readstate && newstate)
- cur_ops->read_delay(trsp);
+ cur_ops->read_delay(trsp, rtrsp);
/* Update the reader state. */
if (idxnew == -1)
@@ -1189,11 +1214,11 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp)
{
int mask = rcutorture_extend_mask_max();
unsigned long randmask1 = torture_random(trsp) >> 8;
- unsigned long randmask2 = randmask1 >> 1;
+ unsigned long randmask2 = randmask1 >> 3;
WARN_ON_ONCE(mask >> RCUTORTURE_RDR_SHIFT);
- /* Half the time lots of bits, half the time only one bit. */
- if (randmask1 & 0x1)
+ /* Most of the time lots of bits, half the time only one bit. */
+ if (!(randmask1 & 0x7))
mask = mask & randmask2;
else
mask = mask & (1 << (randmask2 % RCUTORTURE_RDR_NBITS));
@@ -1213,20 +1238,25 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp)
* Do a randomly selected number of extensions of an existing RCU read-side
* critical section.
*/
-static void rcutorture_loop_extend(int *readstate,
- struct torture_random_state *trsp)
+static struct rt_read_seg *
+rcutorture_loop_extend(int *readstate, struct torture_random_state *trsp,
+ struct rt_read_seg *rtrsp)
{
int i;
+ int j;
int mask = rcutorture_extend_mask_max();
WARN_ON_ONCE(!*readstate); /* -Existing- RCU read-side critsect! */
if (!((mask - 1) & mask))
- return; /* Current RCU reader not extendable. */
- i = (torture_random(trsp) >> 3) & RCUTORTURE_RDR_MAX_LOOPS;
- while (i--) {
+ return rtrsp; /* Current RCU reader not extendable. */
+ /* Bias towards larger numbers of loops. */
+ i = (torture_random(trsp) >> 3);
+ i = ((i | (i >> 3)) & RCUTORTURE_RDR_MAX_LOOPS) + 1;
+ for (j = 0; j < i; j++) {
mask = rcutorture_extend_mask(*readstate, trsp);
- rcutorture_one_extend(readstate, mask, trsp);
+ rcutorture_one_extend(readstate, mask, trsp, &rtrsp[j]);
}
+ return &rtrsp[j];
}
/*
@@ -1236,16 +1266,20 @@ static void rcutorture_loop_extend(int *readstate,
*/
static bool rcu_torture_one_read(struct torture_random_state *trsp)
{
+ int i;
unsigned long started;
unsigned long completed;
int newstate;
struct rcu_torture *p;
int pipe_count;
int readstate = 0;
+ struct rt_read_seg rtseg[RCUTORTURE_RDR_MAX_SEGS] = { { 0 } };
+ struct rt_read_seg *rtrsp = &rtseg[0];
+ struct rt_read_seg *rtrsp1;
unsigned long long ts;
newstate = rcutorture_extend_mask(readstate, trsp);
- rcutorture_one_extend(&readstate, newstate, trsp);
+ rcutorture_one_extend(&readstate, newstate, trsp, rtrsp++);
started = cur_ops->get_gp_seq();
ts = rcu_trace_clock_local();
p = rcu_dereference_check(rcu_torture_current,
@@ -1255,12 +1289,12 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp)
torturing_tasks());
if (p == NULL) {
/* Wait for rcu_torture_writer to get underway */
- rcutorture_one_extend(&readstate, 0, trsp);
+ rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
return false;
}
if (p->rtort_mbtest == 0)
atomic_inc(&n_rcu_torture_mberror);
- rcutorture_loop_extend(&readstate, trsp);
+ rtrsp = rcutorture_loop_extend(&readstate, trsp, rtrsp);
preempt_disable();
pipe_count = p->rtort_pipe_count;
if (pipe_count > RCU_TORTURE_PIPE_LEN) {
@@ -1281,8 +1315,17 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp)
}
__this_cpu_inc(rcu_torture_batch[completed]);
preempt_enable();
- rcutorture_one_extend(&readstate, 0, trsp);
+ rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
WARN_ON_ONCE(readstate & RCUTORTURE_RDR_MASK);
+
+ /* If error or close call, record the sequence of reader protections. */
+ if ((pipe_count > 1 || completed > 1) && !xchg(&err_segs_recorded, 1)) {
+ i = 0;
+ for (rtrsp1 = &rtseg[0]; rtrsp1 < rtrsp; rtrsp1++)
+ err_segs[i++] = *rtrsp1;
+ rt_read_nsegs = i;
+ }
+
return true;
}
@@ -1747,6 +1790,7 @@ static enum cpuhp_state rcutor_hp;
static void
rcu_torture_cleanup(void)
{
+ int firsttime;
int flags = 0;
unsigned long gp_seq = 0;
int i;
@@ -1800,6 +1844,33 @@ rcu_torture_cleanup(void)
rcu_torture_stats_print(); /* -After- the stats thread is stopped! */
+ if (err_segs_recorded) {
+ pr_alert("Failure/close-call rcutorture reader segments:\n");
+ if (rt_read_nsegs == 0)
+ pr_alert("\t: No segments recorded!!!\n");
+ firsttime = 1;
+ for (i = 0; i < rt_read_nsegs; i++) {
+ pr_alert("\t%d: %#x ", i, err_segs[i].rt_readstate);
+ if (err_segs[i].rt_delay_jiffies != 0) {
+ pr_cont("%s%ldjiffies", firsttime ? "" : "+",
+ err_segs[i].rt_delay_jiffies);
+ firsttime = 0;
+ }
+ if (err_segs[i].rt_delay_ms != 0) {
+ pr_cont("%s%ldms", firsttime ? "" : "+",
+ err_segs[i].rt_delay_ms);
+ firsttime = 0;
+ }
+ if (err_segs[i].rt_delay_us != 0) {
+ pr_cont("%s%ldus", firsttime ? "" : "+",
+ err_segs[i].rt_delay_us);
+ firsttime = 0;
+ }
+ pr_cont("%s\n",
+ err_segs[i].rt_preempted ? "preempted" : "");
+
+ }
+ }
if (atomic_read(&n_rcu_torture_error) || n_rcu_torture_barrier_error)
rcu_torture_print_module_parms(cur_ops, "End of test: FAILURE");
else if (torture_onoff_failures())
@@ -1943,6 +2014,8 @@ rcu_torture_init(void)
per_cpu(rcu_torture_batch, cpu)[i] = 0;
}
}
+ err_segs_recorded = 0;
+ rt_read_nsegs = 0;
/* Start up the kthreads. */
|