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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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