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    Subject[PATCH 17/45] FS-Cache: Provide an add_wait_queue_tail() function [ver #35]
    Date
    Provide an add_wait_queue_tail() function to add a waiter to the back of a
    wait queue instead of the front.

    Signed-off-by: David Howells <dhowells@redhat.com>
    ---

    include/linux/pagemap.h | 7 +++++--
    include/linux/wait.h | 1 +
    kernel/wait.c | 18 ++++++++++++++++++
    mm/filemap.c | 2 +-
    4 files changed, 25 insertions(+), 3 deletions(-)


    diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
    index c5df3ae..ad9484f 100644
    --- a/include/linux/pagemap.h
    +++ b/include/linux/pagemap.h
    @@ -225,8 +225,11 @@ static inline void wait_on_page_writeback(struct page *page)

    extern void end_page_writeback(struct page *page);

    -/*
    - * Wait for a PG_owner_priv_2 to become clear
    +/**
    + * wait_on_page_owner_priv_2 - Wait for PG_owner_priv_2 to become clear
    + * @page: The page to monitor
    + *
    + * Wait for a PG_owner_priv_2 to become clear on the specified page.
    */
    static inline void wait_on_page_owner_priv_2(struct page *page)
    {
    diff --git a/include/linux/wait.h b/include/linux/wait.h
    index 0081147..a6a6607 100644
    --- a/include/linux/wait.h
    +++ b/include/linux/wait.h
    @@ -118,6 +118,7 @@ static inline int waitqueue_active(wait_queue_head_t *q)
    #define is_sync_wait(wait) (!(wait) || ((wait)->private))

    extern void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);
    +extern void add_wait_queue_tail(wait_queue_head_t *q, wait_queue_t *wait);
    extern void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait);
    extern void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);

    diff --git a/kernel/wait.c b/kernel/wait.c
    index c275c56..191df0d 100644
    --- a/kernel/wait.c
    +++ b/kernel/wait.c
    @@ -29,6 +29,24 @@ void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
    }
    EXPORT_SYMBOL(add_wait_queue);

    +/**
    + * add_wait_queue_tail - Add a waiter to the back of a waitqueue
    + * @q: the wait queue to append the waiter to
    + * @wait: the waiter to be queued
    + *
    + * Add a waiter to the back of a waitqueue so that it gets woken up last.
    + */
    +void add_wait_queue_tail(wait_queue_head_t *q, wait_queue_t *wait)
    +{
    + unsigned long flags;
    +
    + wait->flags &= ~WQ_FLAG_EXCLUSIVE;
    + spin_lock_irqsave(&q->lock, flags);
    + __add_wait_queue_tail(q, wait);
    + spin_unlock_irqrestore(&q->lock, flags);
    +}
    +EXPORT_SYMBOL(add_wait_queue_tail);
    +
    void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
    {
    unsigned long flags;
    diff --git a/mm/filemap.c b/mm/filemap.c
    index 636adf2..9a0c803 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -586,7 +586,7 @@ void end_page_writeback(struct page *page)
    EXPORT_SYMBOL(end_page_writeback);

    /**
    - * end_page_own - Clear PG_owner_priv_2 and wake up any waiters
    + * end_page_owner_priv_2 - Clear PG_owner_priv_2 and wake up any waiters
    * @page: the page
    *
    * Clear PG_owner_priv_2 and wake up any processes waiting for that event.


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