linux-kernel - Re: [PATCH] sched: Avoid that __wait_on_bit

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Message-ID: <20160810104555.GA3333@redhat.com>
Date:	Wed, 10 Aug 2016 12:45:56 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Bart Van Assche <bart.vanassche@...disk.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Neil Brown <neilb@...e.de>,
	Michael Shaver <jmshaver@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs

On 08/09, Bart Van Assche wrote:
>
> On 08/09/2016 10:15 AM, Oleg Nesterov wrote:
> >
> > --- x/kernel/sched/wait.c
> > +++ x/kernel/sched/wait.c
> > @@ -283,7 +283,7 @@ void abort_exclusive_wait(wait_queue_hea
> >  	if (!list_empty(&wait->task_list))
> >  		list_del_init(&wait->task_list);
> >  	else if (waitqueue_active(q))
> > -		__wake_up_locked_key(q, mode, key);
> > +		__wake_up_locked_key(q, TASK_NORMAL, key);
> >  	spin_unlock_irqrestore(&q->lock, flags);
> >  }
> >  EXPORT_SYMBOL(abort_exclusive_wait);
>
> Hello Oleg,
>
> That patch looks interesting to me.

And I'll redo/resend it, __wake_up_locked_key(mode) is simply wrong I think.

But it can't affect lock_page() because TASK_KILLABLE includes TASK_UNINTERRUPTIBLE
and we do not have lock_page_interruptible().


> Unfortunately even with that patch
> applied I still see lockups.

Thanks. I hoped this change can fix some another exclusive wait...

OK. Could you  try another debugging patch below?

Oleg.
---

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e5a3244..9d5f892 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -711,6 +711,15 @@ static inline int page_has_private(struct page *page)
 	return !!(page->flags & PAGE_FLAGS_PRIVATE);
 }
 
+void unlock_page(struct page *page);
+static inline void __ClearPageLocked_x(struct page *page)
+{
+	if (PageLocked(compound_head(page)))
+		unlock_page(page);
+}
+
+#define __ClearPageLocked(page)	__ClearPageLocked_x(page)
+
 #undef PF_ANY
 #undef PF_HEAD
 #undef PF_NO_TAIL