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    Subject[41/46] sysfs: Allow sysfs_notify_dirent to be called from interrupt context.
    2.6.31-stable review patch.  If anyone has any objections, please let us know.

    ------------------
    From: Neil Brown <neilb@suse.de>

    commit 83db93f4de2d9ae441a491d1dc61c2204f0195de upstream.

    sysfs_notify_dirent is a simple atomic operation that can be used to
    alert user-space that new data can be read from a sysfs attribute.

    Unfortunately it cannot currently be called from non-process context
    because of its use of spin_lock which is sometimes taken with
    interrupts enabled.

    So change all lockers of sysfs_open_dirent_lock to disable interrupts,
    thus making sysfs_notify_dirent safe to be called from non-process
    context (as drivers/md does in md_safemode_timeout).

    sysfs_get_open_dirent is (documented as being) only called from
    process context, so it uses spin_lock_irq. Other places
    use spin_lock_irqsave.

    The usage for sysfs_notify_dirent in md_safemode_timeout was
    introduced in 2.6.28, so this patch is suitable for that and more
    recent kernels.

    Reported-by: Joel Andres Granados <jgranado@redhat.com>
    Signed-off-by: NeilBrown <neilb@suse.de>
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/sysfs/file.c | 14 ++++++++------
    1 file changed, 8 insertions(+), 6 deletions(-)

    --- a/fs/sysfs/file.c
    +++ b/fs/sysfs/file.c
    @@ -268,7 +268,7 @@ static int sysfs_get_open_dirent(struct
    struct sysfs_open_dirent *od, *new_od = NULL;

    retry:
    - spin_lock(&sysfs_open_dirent_lock);
    + spin_lock_irq(&sysfs_open_dirent_lock);

    if (!sd->s_attr.open && new_od) {
    sd->s_attr.open = new_od;
    @@ -281,7 +281,7 @@ static int sysfs_get_open_dirent(struct
    list_add_tail(&buffer->list, &od->buffers);
    }

    - spin_unlock(&sysfs_open_dirent_lock);
    + spin_unlock_irq(&sysfs_open_dirent_lock);

    if (od) {
    kfree(new_od);
    @@ -315,8 +315,9 @@ static void sysfs_put_open_dirent(struct
    struct sysfs_buffer *buffer)
    {
    struct sysfs_open_dirent *od = sd->s_attr.open;
    + unsigned long flags;

    - spin_lock(&sysfs_open_dirent_lock);
    + spin_lock_irqsave(&sysfs_open_dirent_lock, flags);

    list_del(&buffer->list);
    if (atomic_dec_and_test(&od->refcnt))
    @@ -324,7 +325,7 @@ static void sysfs_put_open_dirent(struct
    else
    od = NULL;

    - spin_unlock(&sysfs_open_dirent_lock);
    + spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);

    kfree(od);
    }
    @@ -456,8 +457,9 @@ static unsigned int sysfs_poll(struct fi
    void sysfs_notify_dirent(struct sysfs_dirent *sd)
    {
    struct sysfs_open_dirent *od;
    + unsigned long flags;

    - spin_lock(&sysfs_open_dirent_lock);
    + spin_lock_irqsave(&sysfs_open_dirent_lock, flags);

    od = sd->s_attr.open;
    if (od) {
    @@ -465,7 +467,7 @@ void sysfs_notify_dirent(struct sysfs_di
    wake_up_interruptible(&od->poll);
    }

    - spin_unlock(&sysfs_open_dirent_lock);
    + spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
    }
    EXPORT_SYMBOL_GPL(sysfs_notify_dirent);




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