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    Subject[PATCH] fbmem: fix race condition between register_framebuffer() and fb_open()
    Date
    register_framebuffer() acquires registration_lock, then calls
    do_register_framebuffer() which calls fb_notifier_call_chain()
    which calls fb_open() which calls get_fb_info() which tries
    (at last) to acquire registration_lock again.
    This is a workaround.

    Signed-off-by: Fabio Erculiani <lxnay@sabayon.org>
    ---
    drivers/video/fbmem.c | 13 ++++++++++++-
    1 files changed, 12 insertions(+), 1 deletions(-)

    diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
    index 5aac00e..b9831a0 100644
    --- a/drivers/video/fbmem.c
    +++ b/drivers/video/fbmem.c
    @@ -1628,6 +1628,11 @@ static int do_register_framebuffer(struct fb_info *fb_info)
    event.info = fb_info;
    if (!lock_fb_info(fb_info))
    return -ENODEV;
    +
    + /* FIXME: unlock registration mutex before registration
    + * notification is sent, in order to avoid deadlock.
    + */
    + mutex_unlock(&registration_lock);
    fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
    unlock_fb_info(fb_info);
    return 0;
    @@ -1692,7 +1697,13 @@ register_framebuffer(struct fb_info *fb_info)

    mutex_lock(&registration_lock);
    ret = do_register_framebuffer(fb_info);
    - mutex_unlock(&registration_lock);
    + if (ret != 0)
    + /*
    + * FIXME: mutex is unlocked only if ret == 0.
    + * This is the second part of the workaround
    + * that prevents deadlocking.
    + */
    + mutex_unlock(&registration_lock);

    return ret;
    }
    --
    1.7.5.rc1


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