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Message-Id: <20180626000859.23572-16-paulmck@linux.vnet.ibm.com>
Date: Mon, 25 Jun 2018 17:08:35 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 16/40] rcu: Make RCU CPU stall warnings use ->gp_seq
This commit makes the RCU CPU stall-warning code in print_other_cpu_stall(),
print_cpu_stall(), and check_cpu_stall() use ->gp_seq instead of ->gpnum
and ->completed.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
kernel/rcu/tree.c | 51 ++++++++++++++++++++--------------------
kernel/rcu/tree_plugin.h | 8 +++----
2 files changed, 30 insertions(+), 29 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6f9a564e82d3..9452842e0590 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1340,7 +1340,7 @@ static inline void panic_on_rcu_stall(void)
panic("RCU Stall\n");
}
-static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
+static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gp_seq)
{
int cpu;
unsigned long flags;
@@ -1350,6 +1350,8 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
struct rcu_node *rnp = rcu_get_root(rsp);
long totqlen = 0;
+ WARN_ON_ONCE(gp_seq & 0x2); /* Remove when ->gpnum removed. */
+
/* Kick and suppress, if so configured. */
rcu_stall_kick_kthreads(rsp);
if (rcu_cpu_stall_suppress)
@@ -1380,17 +1382,16 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
for_each_possible_cpu(cpu)
totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
cpu)->cblist);
- pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
+ pr_cont("(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
smp_processor_id(), (long)(jiffies - rsp->gp_start),
- (long)rsp->gpnum, (long)rsp->completed, totqlen);
+ (long)rcu_seq_current(&rsp->gp_seq), totqlen);
if (ndetected) {
rcu_dump_cpu_stacks(rsp);
/* Complain about tasks blocking the grace period. */
rcu_print_detail_task_stall(rsp);
} else {
- if (READ_ONCE(rsp->gpnum) != gpnum ||
- READ_ONCE(rsp->completed) == gpnum) {
+ if (rcu_seq_current(&rsp->gp_seq) != gp_seq) {
pr_err("INFO: Stall ended before state dump start\n");
} else {
j = jiffies;
@@ -1442,9 +1443,9 @@ static void print_cpu_stall(struct rcu_state *rsp)
for_each_possible_cpu(cpu)
totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
cpu)->cblist);
- pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
+ pr_cont(" (t=%lu jiffies g=%ld q=%lu)\n",
jiffies - rsp->gp_start,
- (long)rsp->gpnum, (long)rsp->completed, totqlen);
+ (long)rcu_seq_current(&rsp->gp_seq), totqlen);
rcu_check_gp_kthread_starvation(rsp);
@@ -1471,8 +1472,8 @@ static void print_cpu_stall(struct rcu_state *rsp)
static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
- unsigned long completed;
- unsigned long gpnum;
+ unsigned long gs1;
+ unsigned long gs2;
unsigned long gps;
unsigned long j;
unsigned long jn;
@@ -1488,28 +1489,28 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
/*
* Lots of memory barriers to reject false positives.
*
- * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
- * then rsp->gp_start, and finally rsp->completed. These values
- * are updated in the opposite order with memory barriers (or
- * equivalent) during grace-period initialization and cleanup.
- * Now, a false positive can occur if we get an new value of
- * rsp->gp_start and a old value of rsp->jiffies_stall. But given
- * the memory barriers, the only way that this can happen is if one
- * grace period ends and another starts between these two fetches.
- * Detect this by comparing rsp->completed with the previous fetch
- * from rsp->gpnum.
+ * The idea is to pick up rsp->gp_seq, then rsp->jiffies_stall,
+ * then rsp->gp_start, and finally another copy of rsp->gp_seq.
+ * These values are updated in the opposite order with memory
+ * barriers (or equivalent) during grace-period initialization
+ * and cleanup. Now, a false positive can occur if we get an new
+ * value of rsp->gp_start and a old value of rsp->jiffies_stall.
+ * But given the memory barriers, the only way that this can happen
+ * is if one grace period ends and another starts between these
+ * two fetches. This is detected by comparing the second fetch
+ * of rsp->gp_seq with the previous fetch from rsp->gp_seq.
*
* Given this check, comparisons of jiffies, rsp->jiffies_stall,
* and rsp->gp_start suffice to forestall false positives.
*/
- gpnum = READ_ONCE(rsp->gpnum);
- smp_rmb(); /* Pick up ->gpnum first... */
+ gs1 = READ_ONCE(rsp->gp_seq);
+ smp_rmb(); /* Pick up ->gp_seq first... */
js = READ_ONCE(rsp->jiffies_stall);
smp_rmb(); /* ...then ->jiffies_stall before the rest... */
gps = READ_ONCE(rsp->gp_start);
- smp_rmb(); /* ...and finally ->gp_start before ->completed. */
- completed = READ_ONCE(rsp->completed);
- if (ULONG_CMP_GE(completed, gpnum) ||
+ smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
+ gs2 = READ_ONCE(rsp->gp_seq);
+ if (gs1 != gs2 ||
ULONG_CMP_LT(j, js) ||
ULONG_CMP_GE(gps, js))
return; /* No stall or GP completed since entering function. */
@@ -1527,7 +1528,7 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
/* They had a few time units to dump stack, so complain. */
- print_other_cpu_stall(rsp, gpnum);
+ print_other_cpu_stall(rsp, gs2);
}
}
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 2036dc7426ac..f4a88e3c388d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1755,12 +1755,12 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
*/
touch_nmi_watchdog();
- if (rsp->gpnum == rdp->gpnum) {
+ ticks_value = rcu_seq_ctr(rsp->gp_seq - rdp->gp_seq);
+ if (ticks_value) {
+ ticks_title = "GPs behind";
+ } else {
ticks_title = "ticks this GP";
ticks_value = rdp->ticks_this_gp;
- } else {
- ticks_title = "GPs behind";
- ticks_value = rsp->gpnum - rdp->gpnum;
}
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
--
2.17.1
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