From c41247e1d4864c863ee25e029dd53acdb2abc000 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 5 May 2014 08:18:30 -0700 Subject: [PATCH] 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 Signed-off-by: Paul E. McKenney Acked-by: Oleg Nesterov Reviewed-by: Lai Jiangshan --- kernel/signal.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/signal.c b/kernel/signal.c index a4077e90f19f..40b76e351e64 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);