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| author |   Joel Fernandes (Google) <joel@joelfernandes.org> | 2020-09-29 15:29:27 -0400 |
|---|---|---|
| committer |   Paul E. McKenney <paulmck@kernel.org> | 2020-11-19 19:37:16 -0800 |
| commit | 9f866dac94292f93d3b6bf8dbe860a44b954e555 (patch) | |
| tree | ee1501cd37a82004b9d9b590d033d6efa40e93ee /kernel/rcu | |
| parent | rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config (diff) | |
| download | linux-dev-9f866dac94292f93d3b6bf8dbe860a44b954e555.tar.xz linux-dev-9f866dac94292f93d3b6bf8dbe860a44b954e555.zip | |
rcu/tree: Add a warning if CPU being onlined did not report QS already
Currently, rcu_cpu_starting() checks to see if the RCU core expects a
quiescent state from the incoming CPU. However, the current interaction
between RCU quiescent-state reporting and CPU-hotplug operations should
mean that the incoming CPU never needs to report a quiescent state.
First, the outgoing CPU reports a quiescent state if needed. Second,
the race where the CPU is leaving just as RCU is initializing a new
grace period is handled by an explicit check for this condition. Third,
the CPU's leaf rcu_node structure's ->lock serializes these checks.
This means that if rcu_cpu_starting() ever feels the need to report
a quiescent state, then there is a bug somewhere in the CPU hotplug
code or the RCU grace-period handling code. This commit therefore
adds a WARN_ON_ONCE() to bring that bug to everyone's attention.
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 39e14cf6a9c0..e4d6d0b1b853 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4075,7 +4075,9 @@ void rcu_cpu_starting(unsigned int cpu) rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */ rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq); rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags); - if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */ + + /* An incoming CPU should never be blocking a grace period. */ + if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */ rcu_disable_urgency_upon_qs(rdp); /* Report QS -after- changing ->qsmaskinitnext! */ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); |