From 59dc6f3c6d81c0c4379025c4eb56919391d62b67 Mon Sep 17 00:00:00 2001 From: Anna-Maria Gleixner Date: Fri, 25 May 2018 11:05:07 +0200 Subject: [PATCH] signal: Remove no longer required irqsave/restore 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 b4abf91047cf ("rtmutex: Make wait_lock irq safe") for a different reason. Therefore revert commit a841796f11c9 ("signal: align > __lock_task_sighand() irq disabling and RCU") as the interrupt disable dance is not longer required. The change was tested on the base of b4abf91047cf ("rtmutex: Make wait_lock irq safe") with a four hour run of rcutorture scenario TREE03 with lockdep enabled as suggested by Paul McKenney. Signed-off-by: Anna-Maria Gleixner Signed-off-by: Thomas Gleixner Acked-by: Paul E. McKenney Acked-by: "Eric W. Biederman" Cc: bigeasy@linutronix.de Link: https://lkml.kernel.org/r/20180525090507.22248-3-anna-maria@linutronix.de --- kernel/signal.c | 24 +++++++----------------- 1 file changed, 7 insertions(+), 17 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index 0f865d67415d54..8d8a940422a8e0 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; }