On Wed, Aug 15, 2018 at 05:44:05PM +0200, Mike Galbraith wrote:
>
> 1e64b15a4b10 ("rcu: Fix grace-period hangs due to race with CPU offline")
> added spinlock_t ofl_lock to the rcu_state structure, then takes it with
> preemption disabled during CPU offline, giving RT sleeping lock heartburn.
>
> Convert it to raw_spinlock_t.
>
> Signed-off-by: Mike Galbraith <efa...@gmx.de>
Good catch, applied and started testing.
I had to hand-apply this one due to the RCU flavor consolidation churn.
Let's just say that your patch is the 160th in -rcu slated for the next
merge window, putting us about 30% of the way to the Greg KH criterion. ;-)
(That said, about 25 of those patches are LKMM rather than RCU.)
So please see below for my adaptation of your patch. Please let me know
if I messed anything up.
Thanx, Paul
------------------------------------------------------------------------
commit f5bc811f274bb5ff6da5f84f6928d00711c28f09
Author: Mike Galbraith <efa...@gmx.de>
Date: Wed Aug 15 09:05:29 2018 -0700
rcu: Convert rcu_state.ofl_lock to raw_spinlock_t
1e64b15a4b10 ("rcu: Fix grace-period hangs due to race with CPU offline")
added spinlock_t ofl_lock to the rcu_state structure, then takes it with
preemption disabled during CPU offline, which gives the -rt patchset's
sleeping spinlock heartburn.
This commit therefore converts ->ofl_lock to raw_spinlock_t.
Signed-off-by: Mike Galbraith <efa...@gmx.de>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Sebastian Andrzej Siewior <bige...@linutronix.de>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index bf016ff9f873..7f7008dd9c34 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -97,7 +97,7 @@ struct rcu_state rcu_state = {
.abbr = RCU_ABBR,
.exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
.exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
- .ofl_lock = __SPIN_LOCK_UNLOCKED(rcu_state.ofl_lock),
+ .ofl_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.ofl_lock),
};
/* Dump rcu_node combining tree at boot to verify correct setup. */
@@ -1775,13 +1775,13 @@ static bool rcu_gp_init(void)
*/
rcu_state.gp_state = RCU_GP_ONOFF;
rcu_for_each_leaf_node(rnp) {
- spin_lock(&rcu_state.ofl_lock);
+ raw_spin_lock(&rcu_state.ofl_lock);
raw_spin_lock_irq_rcu_node(rnp);
if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
!rnp->wait_blkd_tasks) {
/* Nothing to do on this leaf rcu_node structure. */
raw_spin_unlock_irq_rcu_node(rnp);
- spin_unlock(&rcu_state.ofl_lock);
+ raw_spin_unlock(&rcu_state.ofl_lock);
continue;
}
@@ -1817,7 +1817,7 @@ static bool rcu_gp_init(void)
}
raw_spin_unlock_irq_rcu_node(rnp);
- spin_unlock(&rcu_state.ofl_lock);
+ raw_spin_unlock(&rcu_state.ofl_lock);
}
rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
@@ -3376,7 +3376,7 @@ void rcu_report_dead(unsigned int cpu)
/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
mask = rdp->grpmask;
- spin_lock(&rcu_state.ofl_lock);
+ raw_spin_lock(&rcu_state.ofl_lock);
raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order
guarantee. */
rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
@@ -3387,7 +3387,7 @@ void rcu_report_dead(unsigned int cpu)
}
rnp->qsmaskinitnext &= ~mask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- spin_unlock(&rcu_state.ofl_lock);
+ raw_spin_unlock(&rcu_state.ofl_lock);
per_cpu(rcu_cpu_started, cpu) = 0;
}
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index bfbf97a1c29d..703e19ff532d 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -343,7 +343,7 @@ struct rcu_state {
const char *name; /* Name of structure. */
char abbr; /* Abbreviated name. */
- spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
+ raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
/* Synchronize offline with */
/* GP pre-initialization. */
};
