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    Subject[PATCH 50/67] fscache: Make fscache_clear_page_bits() conditional on cookie
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    Make fscache_clear_page_bits() conditional on cookie not being NULL, rather
    than merely conditional on CONFIG_FSCACHE=[ym]. The problem with the
    latter is if a filesystem, say afs, has CONFIG_AFS_FSCACHE=n but calls into
    this function - in which it linkage will fail if CONFIG_FSCACHE is less
    than CONFIG_AFS. Analogous problems can affect other filesystems, e.g. 9p.

    Making fscache_clear_page_bits() conditional on the cookie achieves two
    things:

    (1) If cookie optimised down to constant NULL, the rest of the function is
    thrown away and the slow path is never called.

    (2) __fscache_clear_page_bits() isn't called if there's no cookie - and
    so, in such a case, the pages won't iterated over attempting to clear
    PG_fscache bits that haven't been set.

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

    fs/fscache/io.c | 5 +++--
    include/linux/fscache.h | 8 +++++---
    2 files changed, 8 insertions(+), 5 deletions(-)

    diff --git a/fs/fscache/io.c b/fs/fscache/io.c
    index 3910cba65545..bc8d1ac0e85c 100644
    --- a/fs/fscache/io.c
    +++ b/fs/fscache/io.c
    @@ -316,7 +316,8 @@ static void fscache_wreq_done(void *priv, ssize_t transferred_or_error,
    {
    struct fscache_write_request *wreq = priv;

    - fscache_clear_page_bits(wreq->mapping, wreq->start, wreq->len);
    + fscache_clear_page_bits(fscache_cres_cookie(&wreq->cache_resources),
    + wreq->mapping, wreq->start, wreq->len);

    if (wreq->term_func)
    wreq->term_func(wreq->term_func_priv, transferred_or_error,
    @@ -373,7 +374,7 @@ void __fscache_write_to_cache(struct fscache_cookie *cookie,
    abandon_free:
    kfree(wreq);
    abandon:
    - fscache_clear_page_bits(mapping, start, len);
    + fscache_clear_page_bits(cookie, mapping, start, len);
    if (term_func)
    term_func(term_func_priv, ret, false);
    }
    diff --git a/include/linux/fscache.h b/include/linux/fscache.h
    index fe4d588641da..847c076d05a6 100644
    --- a/include/linux/fscache.h
    +++ b/include/linux/fscache.h
    @@ -549,6 +549,7 @@ int fscache_write(struct netfs_cache_resources *cres,

    /**
    * fscache_clear_page_bits - Clear the PG_fscache bits from a set of pages
    + * @cookie: The cookie representing the cache object
    * @mapping: The netfs inode to use as the source
    * @start: The start position in @mapping
    * @len: The amount of data to unlock
    @@ -556,10 +557,11 @@ int fscache_write(struct netfs_cache_resources *cres,
    * Clear the PG_fscache flag from a sequence of pages and wake up anyone who's
    * waiting.
    */
    -static inline void fscache_clear_page_bits(struct address_space *mapping,
    +static inline void fscache_clear_page_bits(struct fscache_cookie *cookie,
    + struct address_space *mapping,
    loff_t start, size_t len)
    {
    - if (fscache_available())
    + if (fscache_cookie_valid(cookie))
    __fscache_clear_page_bits(mapping, start, len);
    }

    @@ -595,7 +597,7 @@ static inline void fscache_write_to_cache(struct fscache_cookie *cookie,
    __fscache_write_to_cache(cookie, mapping, start, len, i_size,
    term_func, term_func_priv);
    } else {
    - fscache_clear_page_bits(mapping, start, len);
    + fscache_clear_page_bits(cookie, mapping, start, len);
    if (term_func)
    term_func(term_func_priv, -ENOBUFS, false);
    }

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