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    SubjectRe: [PATCH 09/12] remove race between use and initialization of locks
    On Tue, 26 Jun 2007 14:50:12 -0400 "Ed L. Cashin" <ecashin@coraid.com> wrote:

    > This change was originally submitted by Alexey Dobriyan in an email
    > with ...
    >
    > Message-ID: <20070325190221.GA5308@martell.zuzino.mipt.ru>
    >
    > and the comment,
    >
    > Some drivers do register_chrdev() before lock or semaphore used in
    > corresponding file_operations is initialized.
    >
    > Andrew Morton commented that these locks should be initialized at
    > compile time, but Alexey Debriyan pointed out that the Documentation
    > tells us to use dynamic initialization whenever possible, and then the
    > discussion petered out.
    >
    > http://preview.tinyurl.com/2pxq6p
    >
    > I believe we made these locks dynamic because of the notice in
    > Documentation/spinlocks.txt, which says that static initializers are
    > deprecated:
    >
    > UPDATE March 21 2005 Amit Gud <gud@eth.net>
    >
    > Macros SPIN_LOCK_UNLOCKED and RW_LOCK_UNLOCKED are deprecated and will be
    > removed soon. So for any new code dynamic initialization should be used:

    The document is inaccurate.

    Yes, the use of SPIN_LOCK_UNLOCKED should be avoided because it breaks
    lockdep. But it can be replaced with DEFINE_SPINLOCK: there is no need to
    switch to runtime initialisation.



    > ...
    >
    > In any case, the patch below makes the code correct and in keeping
    > with the existing documentation. If the existing docs are wrong, I'd
    > be happy to follow up with a patch that corrects them and makes these
    > aoechr.c locks static.
    >
    > Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
    > Signed-off-by: Ed L. Cashin <ecashin@coraid.com>
    > ---
    > drivers/block/aoe/aoechr.c | 4 ++--
    > 1 files changed, 2 insertions(+), 2 deletions(-)
    >
    > diff --git a/drivers/block/aoe/aoechr.c b/drivers/block/aoe/aoechr.c
    > index 10b38a7..2b4f873 100644
    > --- a/drivers/block/aoe/aoechr.c
    > +++ b/drivers/block/aoe/aoechr.c
    > @@ -256,13 +256,13 @@ aoechr_init(void)
    > {
    > int n, i;
    >
    > + sema_init(&emsgs_sema, 0);
    > + spin_lock_init(&emsgs_lock);
    > n = register_chrdev(AOE_MAJOR, "aoechr", &aoe_fops);
    > if (n < 0) {
    > printk(KERN_ERR "aoe: can't register char device\n");
    > return n;
    > }
    > - sema_init(&emsgs_sema, 0);
    > - spin_lock_init(&emsgs_lock);
    > aoe_class = class_create(THIS_MODULE, "aoe");
    > if (IS_ERR(aoe_class)) {
    > unregister_chrdev(AOE_MAJOR, "aoechr");
    > --
    > 1.5.2.1
    >
    > -
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