Messages in this thread Patch in this message | | | Date | Thu, 5 Apr 2012 15:26:04 -0700 | From | "Paul E. McKenney" <> | Subject | [PATCH tip/urgent] rcu: Permit call_rcu() from CPU_DYING notifiers |
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As of commit 29494be7, RCU adopts callbacks from the dying CPU in its CPU_DYING notifier, which means that any callbacks posted by later CPU_DYING notifiers are ignored until the CPU comes back online. A WARN_ON_ONCE() was added to __call_rcu() by commit e5601400 to check for this condition. Although this condition did not trigger (at least as far as know) during -next testing, it did recently trigger in mainline (https://lkml.org/lkml/2012/4/2/34).
This commit therefore causes RCU's CPU_DEAD notifier to adopt any callbacks that were posted by CPU_DYING notifiers and removes the WARN_ON_ONCE() from __call_rcu(). A more targeted warning for callback posting from offline CPUs will be added as a separate commit.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
rcutree.c | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 1050d6d..4c927e6 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1406,11 +1406,41 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { unsigned long flags; + int i; unsigned long mask; int need_report = 0; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rnp. */ + /* If a CPU_DYING notifier has enqueued callbacks, adopt them. */ + if (rdp->nxtlist != NULL) { + struct rcu_data *receive_rdp; + + local_irq_save(flags); + receive_rdp = per_cpu_ptr(rsp->rda, smp_processor_id()); + + /* Adjust the counts. */ + receive_rdp->qlen_lazy += rdp->qlen_lazy; + receive_rdp->qlen += rdp->qlen; + rdp->qlen_lazy = 0; + rdp->qlen = 0; + + /* + * Adopt all callbacks. The outgoing CPU was in no shape + * to advance them, so make them all go through a full + * grace period. + */ + *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist; + receive_rdp->nxttail[RCU_NEXT_TAIL] = + rdp->nxttail[RCU_NEXT_TAIL]; + local_irq_restore(flags); + + /* Initialize the outgoing CPU's callback list. */ + rdp->nxtlist = NULL; + for (i = 0; i < RCU_NEXT_SIZE; i++) + rdp->nxttail[i] = &rdp->nxtlist; + } + /* Adjust any no-longer-needed kthreads. */ rcu_stop_cpu_kthread(cpu); rcu_node_kthread_setaffinity(rnp, -1); @@ -1820,7 +1850,6 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), * a quiescent state betweentimes. */ local_irq_save(flags); - WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); rdp = this_cpu_ptr(rsp->rda); /* Add the callback to our list. */
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