From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: minyard@acm.org, linux-rt-users@vger.kernel.org,
Corey Minyard <cminyard@mvista.com>,
linux-kernel@vger.kernel.org, tglx@linutronix.de,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH RT v2] Fix a lockup in wait_for_completion() and friends
Date: Tue, 14 May 2019 10:43:56 +0200 [thread overview]
Message-ID: <20190514084356.GJ2589@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190509161925.kul66w54wpjcinuc@linutronix.de>
On Thu, May 09, 2019 at 06:19:25PM +0200, Sebastian Andrzej Siewior wrote:
> On 2019-05-08 15:57:28 [-0500], minyard@acm.org wrote:
> > kernel/sched/completion.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
> > index 755a58084978..4f9b4cc0c95a 100644
> > --- a/kernel/sched/completion.c
> > +++ b/kernel/sched/completion.c
> > @@ -70,20 +70,20 @@ do_wait_for_common(struct completion *x,
> > long (*action)(long), long timeout, int state)
> > {
> > if (!x->done) {
> > - DECLARE_SWAITQUEUE(wait);
> > -
> > - __prepare_to_swait(&x->wait, &wait);
>
> you can keep DECLARE_SWAITQUEUE remove just __prepare_to_swait()
>
> > do {
> > + DECLARE_SWAITQUEUE(wait);
> > +
> > if (signal_pending_state(state, current)) {
> > timeout = -ERESTARTSYS;
> > break;
> > }
> > + __prepare_to_swait(&x->wait, &wait);
>
> add this, yes and you are done.
>
> > __set_current_state(state);
> > raw_spin_unlock_irq(&x->wait.lock);
> > timeout = action(timeout);
> > raw_spin_lock_irq(&x->wait.lock);
> > + __finish_swait(&x->wait, &wait);
> > } while (!x->done && timeout);
> > - __finish_swait(&x->wait, &wait);
> > if (!x->done)
> > return timeout;
> > }
Now.. that will fix it, but I think it is also wrong.
The problem being that it violates FIFO, something that might be more
important on -RT than elsewhere.
The regular wait API seems confused/inconsistent when it uses
autoremove_wake_function and default_wake_function, which doesn't help,
but we can easily support this with swait -- the problematic thing is
the custom wake functions, we musn't do that.
(also, mingo went and renamed a whole bunch of wait_* crap and didn't do
the same to swait_ so now its named all different :/)
Something like the below perhaps.
---
diff --git a/include/linux/swait.h b/include/linux/swait.h
index 73e06e9986d4..f194437ae7d2 100644
--- a/include/linux/swait.h
+++ b/include/linux/swait.h
@@ -61,11 +61,13 @@ struct swait_queue_head {
struct swait_queue {
struct task_struct *task;
struct list_head task_list;
+ unsigned int remove;
};
#define __SWAITQUEUE_INITIALIZER(name) { \
.task = current, \
.task_list = LIST_HEAD_INIT((name).task_list), \
+ .remove = 1, \
}
#define DECLARE_SWAITQUEUE(name) \
diff --git a/kernel/sched/swait.c b/kernel/sched/swait.c
index e83a3f8449f6..86974ecbabfc 100644
--- a/kernel/sched/swait.c
+++ b/kernel/sched/swait.c
@@ -28,7 +28,8 @@ void swake_up_locked(struct swait_queue_head *q)
curr = list_first_entry(&q->task_list, typeof(*curr), task_list);
wake_up_process(curr->task);
- list_del_init(&curr->task_list);
+ if (curr->remove)
+ list_del_init(&curr->task_list);
}
EXPORT_SYMBOL(swake_up_locked);
@@ -57,7 +58,8 @@ void swake_up_all(struct swait_queue_head *q)
curr = list_first_entry(&tmp, typeof(*curr), task_list);
wake_up_state(curr->task, TASK_NORMAL);
- list_del_init(&curr->task_list);
+ if (curr->remove)
+ list_del_init(&curr->task_list);
if (list_empty(&tmp))
break;
next prev parent reply other threads:[~2019-05-14 8:44 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190508205728.25557-1-minyard@acm.org>
2019-05-09 16:19 ` [PATCH RT v2] Fix a lockup in wait_for_completion() and friends Sebastian Andrzej Siewior
2019-05-09 17:46 ` Corey Minyard
2019-05-14 8:43 ` Peter Zijlstra [this message]
2019-05-14 9:12 ` Sebastian Andrzej Siewior
2019-05-14 11:35 ` Peter Zijlstra
2019-05-14 15:25 ` Sebastian Andrzej Siewior
2019-05-14 12:13 ` Corey Minyard
2019-05-14 15:36 ` Sebastian Andrzej Siewior
2019-05-15 16:22 ` Corey Minyard
2019-06-26 10:35 ` Peter Zijlstra
2019-05-09 19:33 minyard
2019-05-09 19:51 ` Steven Rostedt
2019-05-10 10:33 ` Sebastian Andrzej Siewior
2019-05-10 12:08 ` Corey Minyard
2019-05-10 12:26 ` Sebastian Andrzej Siewior
2019-06-29 1:49 ` Steven Rostedt
2019-07-01 19:09 ` Corey Minyard
2019-07-01 20:18 ` Steven Rostedt
2019-07-01 20:43 ` Corey Minyard
2019-07-01 21:06 ` Steven Rostedt
2019-07-01 21:13 ` Steven Rostedt
2019-07-01 21:28 ` Steven Rostedt
2019-07-01 21:34 ` Corey Minyard
2019-07-02 7:04 ` Kurt Kanzenbach
2019-07-02 8:35 ` Sebastian Andrzej Siewior
2019-07-02 11:40 ` Corey Minyard
2019-07-02 11:53 ` Sebastian Andrzej Siewior
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190514084356.GJ2589@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=bigeasy@linutronix.de \
--cc=cminyard@mvista.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=minyard@acm.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).