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rcu: Make RCU CPU stall warnings use ->gp_seq

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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@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-04-30 13:09:17 -07:00
parent 29365e563b
commit 471f87c3d9
2 changed files with 30 additions and 29 deletions
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51
kernel/rcu/tree.c
View file

@ -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);
}
}

8
kernel/rcu/tree_plugin.h
View file

@ -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);