From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Daniel Wagner <wagi@monom.org>
Cc: stable-rt@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-rt-users@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>,
Tom Zanussi <tom.zanussi@linux.intel.com>,
Clark Williams <williams@redhat.com>
Subject: Re: [PATCH RT 0/1] Linux v4.19.312-rt134-rc2
Date: Tue, 7 May 2024 11:54:07 +0200 [thread overview]
Message-ID: <20240507095407.jAjEuCJ8@linutronix.de> (raw)
In-Reply-To: <5c3ff133-6953-448b-a1e1-6bacbc210e4d@monom.org>
On 2024-05-06 13:00:39 [+0200], Daniel Wagner wrote:
> Hi Sebastian,
Hi Daniel,
> On 06.05.24 12:46, Daniel Wagner wrote:
> > Dear RT Folks,
> >
> > This is the RT stable review cycle of patch 4.19.312-rt134-rc2.
> >
> > Please scream at me if I messed something up. Please test the patches
> > too.
>
> My announce script is not attaching any conflict resolve diffs
> (eventually, I'll fix this). Could have a look if I got the
> kernel/time/timer.c upddate right? This was caused by stable
> including the 030dcdd197d7 ("timers: Prepare support for
> PREEMPT_RT") patch.
I compared mine outcome vs v4.19-rt-next and the diff at the bottom came
out:
- timer_delete_sync() used to have "#if 0" block around
lockdep_assert_preemption_enabled() because the function is not part
of v4.19. You ended up with might_sleep() which is a minor change.
Your queue as of a previous release had the if0 block (in
__del_timer_sync()).
I would say this is minor but looks like a miss-merge. Therefore I
would say it should go back for consistency vs previous release and
not change it due to conflicts.
- The timer_delete_sync() is structured differently with
__del_timer_sync(). That function invokes timer_sync_wait_running()
which drops two locks which are not acquired. That is wrong. It should
have been del_timer_wait_running().
I suggest you apply the diff below to align it with later versions. It
also gets rid of the basep argument in __try_to_del_timer_sync() which
is not really used.
As an alternative I can send you my rebased queue if this makes it
easier for you.
Sebastian
------------------>8-----------------
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1250,25 +1250,6 @@ int del_timer(struct timer_list *timer)
}
EXPORT_SYMBOL(del_timer);
-static int __try_to_del_timer_sync(struct timer_list *timer,
- struct timer_base **basep)
-{
- struct timer_base *base;
- unsigned long flags;
- int ret = -1;
-
- debug_assert_init(timer);
-
- *basep = base = lock_timer_base(timer, &flags);
-
- if (base->running_timer != timer)
- ret = detach_if_pending(timer, base, true);
-
- raw_spin_unlock_irqrestore(&base->lock, flags);
-
- return ret;
-}
-
/**
* try_to_del_timer_sync - Try to deactivate a timer
* @timer: Timer to deactivate
@@ -1288,8 +1269,19 @@ static int __try_to_del_timer_sync(struct timer_list *timer,
int try_to_del_timer_sync(struct timer_list *timer)
{
struct timer_base *base;
+ unsigned long flags;
+ int ret = -1;
- return __try_to_del_timer_sync(timer, &base);
+ debug_assert_init(timer);
+
+ base = lock_timer_base(timer, &flags);
+
+ if (base->running_timer != timer)
+ ret = detach_if_pending(timer, base, true);
+
+ raw_spin_unlock_irqrestore(&base->lock, flags);
+
+ return ret;
}
EXPORT_SYMBOL(try_to_del_timer_sync);
@@ -1366,36 +1358,6 @@ static inline void timer_sync_wait_running(struct timer_base *base) { }
static inline void del_timer_wait_running(struct timer_list *timer) { }
#endif
-static int __del_timer_sync(struct timer_list *timer)
-{
- struct timer_base *base;
- int ret;
-
- /*
- * Must be able to sleep on PREEMPT_RT because of the slowpath in
- * del_timer_wait_running().
- */
-#if 0
- if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(timer->flags & TIMER_IRQSAFE))
- lockdep_assert_preemption_enabled();
-#endif
-
- for (;;) {
- ret = __try_to_del_timer_sync(timer, &base);
- if (ret >= 0)
- return ret;
-
- if (READ_ONCE(timer->flags) & TIMER_IRQSAFE)
- continue;
-
- /*
- * When accessing the lock, timers of base are no longer expired
- * and so timer is no longer running.
- */
- timer_sync_wait_running(base);
- }
-}
-
/**
* timer_delete_sync - Deactivate a timer and wait for the handler to finish.
* @timer: The timer to be deactivated
@@ -1437,6 +1399,8 @@ static int __del_timer_sync(struct timer_list *timer)
*/
int timer_delete_sync(struct timer_list *timer)
{
+ int ret;
+
#ifdef CONFIG_LOCKDEP
unsigned long flags;
@@ -1454,14 +1418,26 @@ int timer_delete_sync(struct timer_list *timer)
* could lead to deadlock.
*/
WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
+
/*
* Must be able to sleep on PREEMPT_RT because of the slowpath in
- * __del_timer_sync().
+ * del_timer_wait_running().
*/
+#if 0
if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(timer->flags & TIMER_IRQSAFE))
- might_sleep();
+ lockdep_assert_preemption_enabled();
+#endif
- return __del_timer_sync(timer);
+ do {
+ ret = try_to_del_timer_sync(timer);
+
+ if (unlikely(ret < 0)) {
+ del_timer_wait_running(timer);
+ cpu_relax();
+ }
+ } while (ret < 0);
+
+ return ret;
}
EXPORT_SYMBOL(timer_delete_sync);
next prev parent reply other threads:[~2024-05-07 9:54 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-06 10:46 [PATCH RT 0/1] Linux v4.19.312-rt134-rc2 Daniel Wagner
2024-05-06 10:46 ` [PATCH RT 1/1] Linux 4.19.312-rt134 Daniel Wagner
2024-05-06 11:00 ` [PATCH RT 0/1] Linux v4.19.312-rt134-rc2 Daniel Wagner
2024-05-07 9:54 ` Sebastian Andrzej Siewior [this message]
2024-05-07 11:11 ` Daniel Wagner
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