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rcu: Eliminate stall-warning use of rsp 

Now that there is only one rcu_state structure, there is less point
in maintaining a pointer to it.  This commit therefore replaces rsp
with &rcu_state in print_other_cpu_stall(), print_cpu_stall(), and
check_cpu_stall().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-07-05 00:02:29 -07:00
parent 7cba4775ba
commit 4c6ed43708
1 changed files with 39 additions and 41 deletions
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80
kernel/rcu/tree.c
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@ -1273,17 +1273,17 @@ static void rcu_dump_cpu_stacks(void)
static void rcu_stall_kick_kthreads(void)
{
unsigned long j;
struct rcu_state *rsp = &rcu_state;
if (!rcu_kick_kthreads)
return;
j = READ_ONCE(rsp->jiffies_kick_kthreads);
if (time_after(jiffies, j) && rsp->gp_kthread &&
(rcu_gp_in_progress() || READ_ONCE(rsp->gp_flags))) {
WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
if (time_after(jiffies, j) && rcu_state.gp_kthread &&
(rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
WARN_ONCE(1, "Kicking %s grace-period kthread\n",
rcu_state.name);
rcu_ftrace_dump(DUMP_ALL);
wake_up_process(rsp->gp_kthread);
WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);
wake_up_process(rcu_state.gp_kthread);
WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
}
}
@ -1301,7 +1301,6 @@ static void print_other_cpu_stall(unsigned long gp_seq)
unsigned long j;
int ndetected = 0;
struct rcu_node *rnp = rcu_get_root();
struct rcu_state *rsp = &rcu_state;
long totqlen = 0;
/* Kick and suppress, if so configured. */
@ -1314,7 +1313,7 @@ static void print_other_cpu_stall(unsigned long gp_seq)
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
pr_err("INFO: %s detected stalls on CPUs/tasks:", rsp->name);
pr_err("INFO: %s detected stalls on CPUs/tasks:", rcu_state.name);
print_cpu_stall_info_begin();
rcu_for_each_leaf_node(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
@ -1334,21 +1333,21 @@ static void print_other_cpu_stall(unsigned long gp_seq)
totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(&rcu_data,
cpu)->cblist);
pr_cont("(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
smp_processor_id(), (long)(jiffies - rsp->gp_start),
(long)rcu_seq_current(&rsp->gp_seq), totqlen);
smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
if (ndetected) {
rcu_dump_cpu_stacks();
/* Complain about tasks blocking the grace period. */
rcu_print_detail_task_stall();
} else {
if (rcu_seq_current(&rsp->gp_seq) != gp_seq) {
if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
pr_err("INFO: Stall ended before state dump start\n");
} else {
j = jiffies;
gpa = READ_ONCE(rsp->gp_activity);
gpa = READ_ONCE(rcu_state.gp_activity);
pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
rsp->name, j - gpa, j, gpa,
rcu_state.name, j - gpa, j, gpa,
jiffies_till_next_fqs,
rcu_get_root()->qsmask);
/* In this case, the current CPU might be at fault. */
@ -1356,8 +1355,8 @@ static void print_other_cpu_stall(unsigned long gp_seq)
}
}
/* Rewrite if needed in case of slow consoles. */
if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
WRITE_ONCE(rsp->jiffies_stall,
if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
WRITE_ONCE(rcu_state.jiffies_stall,
jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
rcu_check_gp_kthread_starvation();
@ -1373,7 +1372,6 @@ static void print_cpu_stall(void)
unsigned long flags;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rcu_get_root();
struct rcu_state *rsp = &rcu_state;
long totqlen = 0;
/* Kick and suppress, if so configured. */
@ -1386,7 +1384,7 @@ static void print_cpu_stall(void)
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
pr_err("INFO: %s self-detected stall on CPU", rsp->name);
pr_err("INFO: %s self-detected stall on CPU", rcu_state.name);
print_cpu_stall_info_begin();
raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
print_cpu_stall_info(smp_processor_id());
@ -1396,8 +1394,8 @@ static void print_cpu_stall(void)
totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(&rcu_data,
cpu)->cblist);
pr_cont(" (t=%lu jiffies g=%ld q=%lu)\n",
jiffies - rsp->gp_start,
(long)rcu_seq_current(&rsp->gp_seq), totqlen);
jiffies - rcu_state.gp_start,
(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
rcu_check_gp_kthread_starvation();
@ -1405,8 +1403,8 @@ static void print_cpu_stall(void)
raw_spin_lock_irqsave_rcu_node(rnp, flags);
/* Rewrite if needed in case of slow consoles. */
if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
WRITE_ONCE(rsp->jiffies_stall,
if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
WRITE_ONCE(rcu_state.jiffies_stall,
jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
@ -1431,7 +1429,6 @@ static void check_cpu_stall(struct rcu_data *rdp)
unsigned long jn;
unsigned long js;
struct rcu_node *rnp;
struct rcu_state *rsp = &rcu_state;
if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
!rcu_gp_in_progress())
@ -1442,27 +1439,28 @@ static void check_cpu_stall(struct rcu_data *rdp)
/*
* Lots of memory barriers to reject false positives.
*
* 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.
* The idea is to pick up rcu_state.gp_seq, then
* rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
* another copy of rcu_state.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 rcu_state.gp_start and a old
* value of rcu_state.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 rcu_state.gp_seq with the
* previous fetch from rcu_state.gp_seq.
*
* Given this check, comparisons of jiffies, rsp->jiffies_stall,
* and rsp->gp_start suffice to forestall false positives.
* Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
* and rcu_state.gp_start suffice to forestall false positives.
*/
gs1 = READ_ONCE(rsp->gp_seq);
gs1 = READ_ONCE(rcu_state.gp_seq);
smp_rmb(); /* Pick up ->gp_seq first... */
js = READ_ONCE(rsp->jiffies_stall);
js = READ_ONCE(rcu_state.jiffies_stall);
smp_rmb(); /* ...then ->jiffies_stall before the rest... */
gps = READ_ONCE(rsp->gp_start);
gps = READ_ONCE(rcu_state.gp_start);
smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
gs2 = READ_ONCE(rsp->gp_seq);
gs2 = READ_ONCE(rcu_state.gp_seq);
if (gs1 != gs2 ||
ULONG_CMP_LT(j, js) ||
ULONG_CMP_GE(gps, js))
@ -1471,14 +1469,14 @@ static void check_cpu_stall(struct rcu_data *rdp)
jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
if (rcu_gp_in_progress() &&
(READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
/* We haven't checked in, so go dump stack. */
print_cpu_stall();
} else if (rcu_gp_in_progress() &&
ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
/* They had a few time units to dump stack, so complain. */
print_other_cpu_stall(gs2);