On 07/08/2014 06:38 AM, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
>
> 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 <o...@redhat.com>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Acked-by: Oleg Nesterov <o...@redhat.com>
> ---
> kernel/signal.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index a4077e90f19f..46161e744760 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.
> + */
A pair of brackets are missing here: rcu_read_unlock()
after that, please add:
Reviewed-by: Lai Jiangshan <la...@cn.fujitsu.com>
It reminds me that I should keep my effort to solve the deadlock
problem where rcu_read_unlock() is overlapped with schedule locks.
> local_irq_save(*flags);
> rcu_read_lock();
> sighand = rcu_dereference(tsk->sighand);
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