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author | Paul E. McKenney <paul.mckenney@linaro.org> | 2011-07-19 10:25:36 (GMT) |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-07-20 18:04:54 (GMT) |
commit | a841796f11c90d53dbac773be56b04fbee8af272 (patch) | |
tree | 9401a53faddecc7c1644565d0e22630028f82bca /kernel | |
parent | ec433f0c51527426989ea8a38a856d810d739414 (diff) | |
download | linux-a841796f11c90d53dbac773be56b04fbee8af272.tar.xz |
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@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel')
-rw-r--r-- | 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; } |