From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org,
linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Carsten Emde <C.Emde@osadl.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
John Kacur <jkacur@redhat.com>, Daniel Wagner <wagi@monom.org>,
Tom Zanussi <zanussi@kernel.org>,
"Srivatsa S. Bhat" <srivatsa@csail.mit.edu>,
Mike Galbraith <efault@gmx.de>,
stable-rt@vger.kernel.org
Subject: [PATCH RT 4/5] timers: Dont block on ->expiry_lock for TIMER_IRQSAFE
Date: Tue, 10 Nov 2020 10:38:57 -0500 [thread overview]
Message-ID: <20201110154025.501654745@goodmis.org> (raw)
In-Reply-To: 20201110153853.463368981@goodmis.org
5.4.74-rt42-rc2 stable review patch.
If anyone has any objections, please let me know.
------------------
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
PREEMPT_RT does not spin and wait until a running timer completes its
callback but instead it blocks on a sleeping lock to prevent a deadlock.
This blocking can not be done for workqueue's IRQ_SAFE timer which will
be canceled in an IRQ-off region. It has to happen to in IRQ-off region
because changing the PENDING bit and clearing the timer must not be
interrupted to avoid a busy-loop.
The callback invocation of IRQSAFE timer is not preempted on PREEMPT_RT
so there is no need to synchronize on timer_base::expiry_lock.
Don't acquire the timer_base::expiry_lock for TIMER_IRQSAFE flagged
timer.
Add a lockdep annotation to ensure that this function is always invoked
in preemptible context on PREEMPT_RT.
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/time/timer.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 89078fd848b9..3e9d7f227a5c 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1289,7 +1289,7 @@ static void del_timer_wait_running(struct timer_list *timer)
u32 tf;
tf = READ_ONCE(timer->flags);
- if (!(tf & TIMER_MIGRATING)) {
+ if (!(tf & (TIMER_MIGRATING | TIMER_IRQSAFE))) {
struct timer_base *base = get_timer_base(tf);
/*
@@ -1373,6 +1373,13 @@ int del_timer_sync(struct timer_list *timer)
*/
WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
+ /*
+ * Must be able to sleep on PREEMPT_RT because of the slowpath in
+ * del_timer_wait_running().
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(timer->flags & TIMER_IRQSAFE))
+ might_sleep();
+
do {
ret = try_to_del_timer_sync(timer);
--
2.28.0
next prev parent reply other threads:[~2020-11-10 15:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-10 15:38 [PATCH RT 0/5] Linux 5.4.74-rt42-rc2 Steven Rostedt
2020-11-10 15:38 ` [PATCH RT 1/5] net: Properly annotate the try-lock for the seqlock Steven Rostedt
2020-11-13 17:06 ` Tom Zanussi
2020-11-13 20:14 ` Tom Zanussi
2020-11-14 19:00 ` Mike Galbraith
2020-11-14 19:24 ` Tom Zanussi
2020-11-15 4:52 ` Mike Galbraith
2020-11-16 17:19 ` Sebastian Andrzej Siewior
2020-11-10 15:38 ` [PATCH RT 2/5] mm/memcontrol: Disable preemption in __mod_memcg_lruvec_state() Steven Rostedt
2020-11-10 15:38 ` [PATCH RT 3/5] ptrace: fix ptrace_unfreeze_traced() race with rt-lock Steven Rostedt
2020-11-10 15:38 ` Steven Rostedt [this message]
2020-11-10 15:38 ` [PATCH RT 5/5] Linux 5.4.74-rt42-rc2 Steven Rostedt
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