From a841796f11c90d53dbac773be56b04fbee8af272 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 19 Jul 2011 03:25:36 -0700 Subject: 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 Signed-off-by: Paul E. McKenney --- kernel/signal.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index ff7678603328..415d85d6f6c6 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; } -- cgit v1.2.3