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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2018-05-15 10:14:34 -0700 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2018-07-12 15:39:02 -0700 |
commit | 5554788e1d4253a92b794a9006b7ae2c10be52af (patch) | |
tree | 854397c8697d9bbf49b789c3177db10dfae498bd /kernel/rcu | |
parent | 928164351e700f91ab588f20fe470cac9db477a9 (diff) | |
download | linux-stable-5554788e1d4253a92b794a9006b7ae2c10be52af.tar.gz linux-stable-5554788e1d4253a92b794a9006b7ae2c10be52af.tar.bz2 linux-stable-5554788e1d4253a92b794a9006b7ae2c10be52af.zip |
rcu: Suppress false-positive offline-CPU lockdep-RCU splat
The rcu_lockdep_current_cpu_online() function currently checks only the
RCU-sched data structures to determine whether or not RCU believes that a
given CPU is offline. Unfortunately, there are multiple flavors of RCU,
which means that there is a short window of time during which the various
flavors disagree as to whether or not a given CPU is offline. This can
result in false-positive lockdep-RCU splats in which some other flavor
of RCU tries to do something based on its view that the CPU is online,
only to get hit with a lockdep-RCU splat because RCU-sched instead
believes that the CPU is offline.
This commit therefore changes rcu_lockdep_current_cpu_online() to scan
all RCU flavors and to consider a given CPU to be online if any of the
RCU flavors believe it to be online, thus preventing these false-positive
splats.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r-- | kernel/rcu/tree.c | 48 |
1 files changed, 24 insertions, 24 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 3efd591fcd15..a7773fc72b0c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1030,41 +1030,41 @@ void rcu_request_urgent_qs_task(struct task_struct *t) #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) /* - * Is the current CPU online? Disable preemption to avoid false positives - * that could otherwise happen due to the current CPU number being sampled, - * this task being preempted, its old CPU being taken offline, resuming - * on some other CPU, then determining that its old CPU is now offline. - * It is OK to use RCU on an offline processor during initial boot, hence - * the check for rcu_scheduler_fully_active. Note also that it is OK - * for a CPU coming online to use RCU for one jiffy prior to marking itself - * online in the cpu_online_mask. Similarly, it is OK for a CPU going - * offline to continue to use RCU for one jiffy after marking itself - * offline in the cpu_online_mask. This leniency is necessary given the - * non-atomic nature of the online and offline processing, for example, - * the fact that a CPU enters the scheduler after completing the teardown - * of the CPU. + * Is the current CPU online as far as RCU is concerned? * - * This is also why RCU internally marks CPUs online during in the - * preparation phase and offline after the CPU has been taken down. + * Disable preemption to avoid false positives that could otherwise + * happen due to the current CPU number being sampled, this task being + * preempted, its old CPU being taken offline, resuming on some other CPU, + * then determining that its old CPU is now offline. Because there are + * multiple flavors of RCU, and because this function can be called in the + * midst of updating the flavors while a given CPU coming online or going + * offline, it is necessary to check all flavors. If any of the flavors + * believe that given CPU is online, it is considered to be online. * - * Disable checking if in an NMI handler because we cannot safely report - * errors from NMI handlers anyway. + * Disable checking if in an NMI handler because we cannot safely + * report errors from NMI handlers anyway. In addition, it is OK to use + * RCU on an offline processor during initial boot, hence the check for + * rcu_scheduler_fully_active. */ bool rcu_lockdep_current_cpu_online(void) { struct rcu_data *rdp; struct rcu_node *rnp; - bool ret; + struct rcu_state *rsp; - if (in_nmi()) + if (in_nmi() || !rcu_scheduler_fully_active) return true; preempt_disable(); - rdp = this_cpu_ptr(&rcu_sched_data); - rnp = rdp->mynode; - ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) || - !rcu_scheduler_fully_active; + for_each_rcu_flavor(rsp) { + rdp = this_cpu_ptr(rsp->rda); + rnp = rdp->mynode; + if (rdp->grpmask & rcu_rnp_online_cpus(rnp)) { + preempt_enable(); + return true; + } + } preempt_enable(); - return ret; + return false; } EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); |