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    SubjectRe: [Linux-cachefs] CacheFiles: Readpage failed on backing file
    At Tue, 04 Aug 2009 18:23:44 +0100,
    David Howells wrote:
    >
    >
    > Takashi Iwai <tiwai@suse.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@suse.de>


    Thanks!

    Takashi

    >
    > David
    > ---
    > From: Peter Zijlstra <peterz@infradead.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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