The value of "fqs_state" in struct rcu_state is always RCU_GP_IDLE.
The real state is stored in a local variable in rcu_gp_kthread().
It is modified by rcu_gp_fqs() via parameter and return value.
But the actual value is never stored to rsp->fqs_state.
The result is that print_one_rcu_state() does not show the real
state.
This code has been added 3 years ago by the commit 4cdfc175c25c89ee
("rcu: Move quiescent-state forcing into kthread"). I guess that it
was an overlook or optimization.
Anyway, the value seems to be manipulated only by the thread, except
for shoving the status. I do not see any risk in updating it directly
in the struct.
Signed-off-by: Petr Mladek <pmla...@suse.com>
---
kernel/rcu/tree.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9f75f25cc5d9..54af8d5f9f7b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1927,16 +1927,15 @@ static bool rcu_gp_fqs_check_wake(struct rcu_state
*rsp, int *gfp)
/*
* Do one round of quiescent-state forcing.
*/
-static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
+static void rcu_gp_fqs(struct rcu_state *rsp)
{
- int fqs_state = fqs_state_in;
bool isidle = false;
unsigned long maxj;
struct rcu_node *rnp = rcu_get_root(rsp);
WRITE_ONCE(rsp->gp_activity, jiffies);
rsp->n_force_qs++;
- if (fqs_state == RCU_SAVE_DYNTICK) {
+ if (rsp->fqs_state == RCU_SAVE_DYNTICK) {
/* Collect dyntick-idle snapshots. */
if (is_sysidle_rcu_state(rsp)) {
isidle = true;
@@ -1945,7 +1944,7 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int
fqs_state_in)
force_qs_rnp(rsp, dyntick_save_progress_counter,
&isidle, &maxj);
rcu_sysidle_report_gp(rsp, isidle, maxj);
- fqs_state = RCU_FORCE_QS;
+ rsp->fqs_state = RCU_FORCE_QS;
} else {
/* Handle dyntick-idle and offline CPUs. */
isidle = true;
@@ -1959,7 +1958,6 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int
fqs_state_in)
READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
raw_spin_unlock_irq(&rnp->lock);
}
- return fqs_state;
}
/*
@@ -2041,7 +2039,6 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
*/
static int __noreturn rcu_gp_kthread(void *arg)
{
- int fqs_state;
int gf;
unsigned long j;
int ret;
@@ -2073,7 +2070,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
}
/* Handle quiescent-state forcing. */
- fqs_state = RCU_SAVE_DYNTICK;
+ rsp->fqs_state = RCU_SAVE_DYNTICK;
j = jiffies_till_first_fqs;
if (j > HZ) {
j = HZ;
@@ -2101,7 +2098,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsstart"));
- fqs_state = rcu_gp_fqs(rsp, fqs_state);
+ rcu_gp_fqs(rsp);
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsend"));
--
1.8.5.6
--
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