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SubjectRe: [PATCH] kernel/signal: Remove no longer required irqsave/restore
Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:

> From: Anna-Maria Gleixner <anna-maria@linutronix.de>
>
> Commit a841796f11c9 ("signal: align __lock_task_sighand() irq disabling and
> RCU") introduced a rcu read side critical section with interrupts
> disabled. The changelog suggested that a better long-term fix would be "to
> make rt_mutex_unlock() disable irqs when acquiring the rt_mutex structure's
> ->wait_lock".
>
> This long-term fix has been made in commit 4abf91047cf ("rtmutex: Make >
> wait_lock irq safe") for different reason.

Which tree has this change been made in? I am not finding the commit
you mention above in Linus's tree.

> Therefore revert commit a841796f11c9 ("signal: align >
> __lock_task_sighand() irq disabling and RCU") as the interrupt disable
> dance is not longer required.

Which tree is change aimed at?

Eric

> Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> kernel/signal.c | 24 +++++++-----------------
> 1 file changed, 7 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index c6e4c83dc090..16b87c54d027 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1244,19 +1244,12 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
> {
> struct sighand_struct *sighand;
>
> + rcu_read_lock();
> 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);
> - if (unlikely(sighand == NULL)) {
> - rcu_read_unlock();
> - local_irq_restore(*flags);
> + if (unlikely(sighand == NULL))
> break;
> - }
> +
> /*
> * This sighand can be already freed and even reused, but
> * we rely on SLAB_TYPESAFE_BY_RCU and sighand_ctor() which
> @@ -1268,15 +1261,12 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
> * __exit_signal(). In the latter case the next iteration
> * must see ->sighand == NULL.
> */
> - spin_lock(&sighand->siglock);
> - if (likely(sighand == tsk->sighand)) {
> - rcu_read_unlock();
> + spin_lock_irqsave(&sighand->siglock, *flags);
> + if (likely(sighand == tsk->sighand))
> break;
> - }
> - spin_unlock(&sighand->siglock);
> - rcu_read_unlock();
> - local_irq_restore(*flags);
> + spin_unlock_irqrestore(&sighand->siglock, *flags);
> }
> + rcu_read_unlock();
>
> return sighand;
> }

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