linux-kernel - Re: [Linux-cachefs] CacheFiles: Readpage failed on backing file

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Date:	Fri, 07 Aug 2009 14:07:51 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	David Howells <dhowells@...hat.com>
Cc:	peterz@...radead.org,
	Linux filesystem caching discussion list 
	<linux-cachefs@...hat.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-cachefs] CacheFiles: Readpage failed on backing file

At Tue, 04 Aug 2009 18:23:44 +0100,
David Howells wrote:
> 
> 
> Takashi Iwai <tiwai@...e.de> wrote:
> 
> > =======================================================
> > [ INFO: possible circular locking dependency detected ]
> > 2.6.30-test #7
> > -------------------------------------------------------
> > swapper/0 is trying to acquire lock:
> >  (&cwq->lock){-.-...}, at: [<c01519f3>] __queue_work+0x1f/0x4e
> > 
> > but task is already holding lock:
> >  (&q->lock){-.-.-.}, at: [<c012cc9c>] __wake_up+0x26/0x5c
> > 
> > which lock already depends on the new lock.
> > ...
> 
> Can you try the attached patch from Peter Zijlstra?  It should cause the work
> queue's waitqueue spinlock to have a separate lockdep class from the page
> bit's waitqueue.

OK, I've been running the patched kernel for a day, and it seems working
fine.  FWIW, I applied your previous fix
    CacheFiles: Handle truncate unlocking the page we're reading
as well.

Tested-by: Takashi Iwai <tiwai@...e.de>


Thanks!

Takashi

> 
> David
> ---
> From: Peter Zijlstra <peterz@...radead.org>
> Subject: [PATCH] Give waitqueue spinlocks their own lockdep classes
> 
> Give waitqueue spinlocks their own lockdep classes when they are initialised
> from init_waitqueue_head().  This means that struct wait_queue::func functions
> can operate other waitqueues.
> 
> This is used by CacheFiles to catch the page from a backing fs being unlocked
> and to wake up another thread to take a copy of it.
> ---
> 
>  include/linux/wait.h |    9 ++++++++-
>  kernel/wait.c        |    5 +++--
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> 
> diff --git a/include/linux/wait.h b/include/linux/wait.h
> index 6788e1a..cf3c2f5 100644
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -77,7 +77,14 @@ struct task_struct;
>  #define __WAIT_BIT_KEY_INITIALIZER(word, bit)				\
>  	{ .flags = word, .bit_nr = bit, }
>  
> -extern void init_waitqueue_head(wait_queue_head_t *q);
> +extern void __init_waitqueue_head(wait_queue_head_t *q, struct lock_class_key *);
> +
> +#define init_waitqueue_head(q)				\
> +	do {						\
> +		static struct lock_class_key __key;	\
> +							\
> +		__init_waitqueue_head((q), &__key);	\
> +	} while (0)
>  
>  #ifdef CONFIG_LOCKDEP
>  # define __WAIT_QUEUE_HEAD_INIT_ONSTACK(name) \
> diff --git a/kernel/wait.c b/kernel/wait.c
> index ea7c3b4..c4bd3d8 100644
> --- a/kernel/wait.c
> +++ b/kernel/wait.c
> @@ -10,13 +10,14 @@
>  #include <linux/wait.h>
>  #include <linux/hash.h>
>  
> -void init_waitqueue_head(wait_queue_head_t *q)
> +void __init_waitqueue_head(wait_queue_head_t *q, struct lock_class_key *key)
>  {
>  	spin_lock_init(&q->lock);
> +	lockdep_set_class(&q->lock, key);
>  	INIT_LIST_HEAD(&q->task_list);
>  }
>  
> -EXPORT_SYMBOL(init_waitqueue_head);
> +EXPORT_SYMBOL(__init_waitqueue_head);
>  
>  void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
>  {
> 
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