Commit-ID: c41247e1d4864c863ee25e029dd53acdb2abc000
Gitweb: http://git.kernel.org/tip/c41247e1d4864c863ee25e029dd53acdb2abc000
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 5 May 2014 08:18:30 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed, 9 Jul 2014 09:14:33 -0700
signal: Explain local_irq_save() call
The explicit local_irq_save() in __lock_task_sighand() is needed to avoid
a potential deadlock condition, as noted in a841796f11c90d53 (signal:
align __lock_task_sighand() irq disabling and RCU). However, someone
reading the code might be forgiven for concluding that this separate
local_irq_save() was completely unnecessary. This commit therefore adds
a comment referencing the shiny new block comment on rcu_read_unlock().
Reported-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Reviewed-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
kernel/signal.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/signal.c b/kernel/signal.c
index a4077e9..40b76e3 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1263,6 +1263,10 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
struct sighand_struct *sighand;
for (;;) {
+ /*
+ * Disable interrupts early to avoid deadlocks.
+ * See rcu_read_unlock() comment header for details.
+ */
local_irq_save(*flags);
rcu_read_lock();
sighand = rcu_dereference(tsk->sighand);
--
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