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    SubjectRe: [uml-devel] Re: [patch 1/1] uml:fix ubd deadlock on SMP
    * BlaisorBlade (blaisorblade_spam@yahoo.it) wrote:
    > Yes, thanks a lot for your help.

    Rename ubd_finish() to __ubd_finsh() and remove ubd_io_lock from it.
    Add wrapper, ubd_finish(), which grabs lock before calling __ubd_finish().
    Update do_ubd_request to use the lock free __ubd_finish() to avoid
    deadlock. Also, apparently prepare_request is called with ubd_io_lock
    held, so remove locks there.

    Signed-off-by: Chris Wright <chrisw@osdl.org>

    ===== arch/um/drivers/ubd_kern.c 1.38 vs edited =====
    --- 1.38/arch/um/drivers/ubd_kern.c 2004-09-07 23:33:13 -07:00
    +++ edited/arch/um/drivers/ubd_kern.c 2004-09-09 12:18:01 -07:00
    @@ -396,14 +396,20 @@
    */
    int intr_count = 0;

    -static void ubd_finish(struct request *req, int error)
    +static inline void ubd_finish(struct request *req, int error)
    +{
    + spin_lock(&ubd_io_lock);
    + __ubd_finish(req, error);
    + spin_unlock(&ubd_io_lock);
    +}
    +
    +/* call ubd_finish if you need to serialize */
    +static void __ubd_finish(struct request *req, int error)
    {
    int nsect;

    if(error){
    - spin_lock(&ubd_io_lock);
    end_request(req, 0);
    - spin_unlock(&ubd_io_lock);
    return;
    }
    nsect = req->current_nr_sectors;
    @@ -412,11 +418,10 @@
    req->errors = 0;
    req->nr_sectors -= nsect;
    req->current_nr_sectors = 0;
    - spin_lock(&ubd_io_lock);
    end_request(req, 1);
    - spin_unlock(&ubd_io_lock);
    }

    +/* Called without ubd_io_lock held */
    static void ubd_handler(void)
    {
    struct io_thread_req req;
    @@ -965,6 +970,7 @@
    return(0);
    }

    +/* Called with ubd_io_lock held */
    static int prepare_request(struct request *req, struct io_thread_req *io_req)
    {
    struct gendisk *disk = req->rq_disk;
    @@ -977,9 +983,7 @@
    if((rq_data_dir(req) == WRITE) && !dev->openflags.w){
    printk("Write attempted on readonly ubd device %s\n",
    disk->disk_name);
    - spin_lock(&ubd_io_lock);
    end_request(req, 0);
    - spin_unlock(&ubd_io_lock);
    return(1);
    }

    @@ -1029,6 +1033,7 @@
    return(0);
    }

    +/* Called with ubd_io_lock held */
    static void do_ubd_request(request_queue_t *q)
    {
    struct io_thread_req io_req;
    @@ -1040,7 +1045,7 @@
    err = prepare_request(req, &io_req);
    if(!err){
    do_io(&io_req);
    - ubd_finish(req, io_req.error);
    + __ubd_finish(req, io_req.error);
    }
    }
    }
    -
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