Commit-ID: a841796f11c90d53dbac773be56b04fbee8af272
Gitweb: http://git.kernel.org/tip/a841796f11c90d53dbac773be56b04fbee8af272
Author: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
AuthorDate: Tue, 19 Jul 2011 03:25:36 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed, 20 Jul 2011 11:04:54 -0700
signal: align __lock_task_sighand() irq disabling and RCU
The __lock_task_sighand() function calls rcu_read_lock() with interrupts
and preemption enabled, but later calls rcu_read_unlock() with interrupts
disabled. It is therefore possible that this RCU read-side critical
section will be preempted and later RCU priority boosted, which means that
rcu_read_unlock() will call rt_mutex_unlock() in order to deboost itself, but
with interrupts disabled. This results in lockdep splats, so this commit
nests the RCU read-side critical section within the interrupt-disabled
region of code. This prevents the RCU read-side critical section from
being preempted, and thus prevents the attempt to deboost with interrupts
disabled.
It is quite possible that a better long-term fix is to make rt_mutex_unlock()
disable irqs when acquiring the rt_mutex structure's ->wait_lock.
Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/signal.c | 19 +++++++++++++------
1 files changed, 13 insertions(+), 6 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index ff76786..415d85d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1178,18 +1178,25 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
{
struct sighand_struct *sighand;
- rcu_read_lock();
for (;;) {
+ local_irq_save(*flags);
+ rcu_read_lock();
sighand = rcu_dereference(tsk->sighand);
- if (unlikely(sighand == NULL))
+ if (unlikely(sighand == NULL)) {
+ rcu_read_unlock();
+ local_irq_restore(*flags);
break;
+ }
- spin_lock_irqsave(&sighand->siglock, *flags);
- if (likely(sighand == tsk->sighand))
+ spin_lock(&sighand->siglock);
+ if (likely(sighand == tsk->sighand)) {
+ rcu_read_unlock();
break;
- spin_unlock_irqrestore(&sighand->siglock, *flags);
+ }
+ spin_unlock(&sighand->siglock);
+ rcu_read_unlock();
+ local_irq_restore(*flags);
}
- rcu_read_unlock();
return sighand;
}
--
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