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rcu: Add diagnostics for offline CPUs failing to report QS

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CPUs are expected to report quiescent states when coming online and
when going offline, and grace-period initialization is supposed to
handle any race conditions where a CPU's ->qsmask bit is set just after
it goes offline.  This commit adds diagnostics for the case where an
offline CPU nevertheless has a grace period waiting on it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-05-15 16:23:23 -07:00
parent fea3f222d3
commit f2e2df5978
2 changed files with 23 additions and 0 deletions
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22
kernel/rcu/tree.c
View file

@ -1188,6 +1188,27 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
smp_store_release(ruqp, true); smp_store_release(ruqp, true);
} }
/* If waiting too long on an offline CPU, complain. */
if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp)) &&
time_after(jiffies, rdp->rsp->gp_start + HZ)) {
bool onl;
struct rcu_node *rnp1;
WARN_ON(1); /* Offline CPUs are supposed to report QS! */
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
__func__, rnp->grplo, rnp->grphi, rnp->level,
(long)rnp->gp_seq, (long)rnp->completedqs);
for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
__func__, rdp->cpu, ".o"[onl],
(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
return 1; /* Break things loose after complaining. */
}
/* /*
* A CPU running for an extended time within the kernel can * A CPU running for an extended time within the kernel can
* delay RCU grace periods. When the CPU is in NO_HZ_FULL mode, * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode,
@ -1967,6 +1988,7 @@ static bool rcu_gp_init(struct rcu_state *rsp)
rnp->grphi, rnp->qsmask); rnp->grphi, rnp->qsmask);
/* Quiescent states for tasks on any now-offline CPUs. */ /* Quiescent states for tasks on any now-offline CPUs. */
mask = rnp->qsmask & ~rnp->qsmaskinitnext; mask = rnp->qsmask & ~rnp->qsmaskinitnext;
rnp->rcu_gp_init_mask = mask;
if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp)) if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags); rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
else else

1
kernel/rcu/tree.h
View file

@ -90,6 +90,7 @@ struct rcu_node {
/* an rcu_data structure, otherwise, each */ /* an rcu_data structure, otherwise, each */
/* bit corresponds to a child rcu_node */ /* bit corresponds to a child rcu_node */
/* structure. */ /* structure. */
unsigned long rcu_gp_init_mask; /* Mask of offline CPUs at GP init. */
unsigned long qsmaskinit; unsigned long qsmaskinit;
/* Per-GP initial value for qsmask. */ /* Per-GP initial value for qsmask. */
/* Initialized from ->qsmaskinitnext at the */ /* Initialized from ->qsmaskinitnext at the */