| Message ID | 1311121103-16978-1-git-send-email-paulmck@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
On Tue, 2011-07-19 at 17:18 -0700, Paul E. McKenney wrote: > +++ b/kernel/rcutree_plugin.h > @@ -696,8 +696,10 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) > raw_spin_lock_irqsave(&rnp->lock, flags); > for (;;) { > if (!sync_rcu_preempt_exp_done(rnp)) > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > break; I bet that'll all work much better if you wrap it in curly braces like: if (!sync_rcu_preempt_exp_done(rnp)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); break; } That might also explain those explosions Ed and Ben have been seeing. > if (rnp->parent == NULL) { > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > wake_up(&sync_rcu_preempt_exp_wq); > break; > } > @@ -707,7 +709,6 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) > raw_spin_lock(&rnp->lock); /* irqs already disabled */ > rnp->expmask &= ~mask; > } > - raw_spin_unlock_irqrestore(&rnp->lock, flags); > }
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 75113cb..94a674e 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -696,8 +696,10 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) raw_spin_lock_irqsave(&rnp->lock, flags); for (;;) { if (!sync_rcu_preempt_exp_done(rnp)) + raw_spin_unlock_irqrestore(&rnp->lock, flags); break; if (rnp->parent == NULL) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); wake_up(&sync_rcu_preempt_exp_wq); break; } @@ -707,7 +709,6 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) raw_spin_lock(&rnp->lock); /* irqs already disabled */ rnp->expmask &= ~mask; } - raw_spin_unlock_irqrestore(&rnp->lock, flags); } /*
PREEMPT_RCU read-side critical sections blocking an expedited grace period invoke rcu_report_exp_rnp(). When the last such critical section has completed, rcu_report_exp_rnp() invokes the scheduler to wake up the task that invoked synchronize_rcu_expedited() -- needlessly holding the root rcu_node structure's lock while doing so, thus needlessly providing a way for RCU and the scheduler to deadlock. This commit therefore releases the root rcu_node structure's lock before calling wake_up(). Reported-by: Ed Tomlinson <edt@aei.ca> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- kernel/rcutree_plugin.h | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-)