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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-05-16 01:23:23 +0200
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2018-07-13 00:39:10 +0200
commitf2e2df59786d7bd52e6e7e2d10c1c6ba433a0ee7 (patch)
tree83228ad0b1384cdb37e5be871f21f9d1cbababc8 /kernel/rcu
parentrcu: Record ->gp_state for both phases of grace-period initialization (diff)
downloadlinux-f2e2df59786d7bd52e6e7e2d10c1c6ba433a0ee7.tar.xz
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rcu: Add diagnostics for offline CPUs failing to report QS
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>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c22
-rw-r--r--kernel/rcu/tree.h1
2 files changed, 23 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ee218d743226..d3333ee2c6f5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1188,6 +1188,27 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
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
* 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);
/* Quiescent states for tasks on any now-offline CPUs. */
mask = rnp->qsmask & ~rnp->qsmaskinitnext;
+ rnp->rcu_gp_init_mask = mask;
if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
else
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 8077aff7ab40..d51e6edc8e83 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -90,6 +90,7 @@ struct rcu_node {
/* an rcu_data structure, otherwise, each */
/* bit corresponds to a child rcu_node */
/* structure. */
+ unsigned long rcu_gp_init_mask; /* Mask of offline CPUs at GP init. */
unsigned long qsmaskinit;
/* Per-GP initial value for qsmask. */
/* Initialized from ->qsmaskinitnext at the */