From: BlaisorBlade <[email protected]>, Chris Wright <[email protected]>
Avoid deadlocking onto the request lock in the UBD driver, i.e. don't lock the
queue spinlock when called from the request function.
In detail:
Rename ubd_finish() to __ubd_finish() 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 <[email protected]>
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <[email protected]>
---
linux-2.6.9-current-paolo/arch/um/drivers/ubd_kern.c | 19 ++++++++++++-------
1 files changed, 12 insertions(+), 7 deletions(-)
diff -puN arch/um/drivers/ubd_kern.c~uml-ubd-deadlock-revised arch/um/drivers/ubd_kern.c
--- linux-2.6.9-current/arch/um/drivers/ubd_kern.c~uml-ubd-deadlock-revised 2004-10-12 01:22:16.360058936 +0200
+++ linux-2.6.9-current-paolo/arch/um/drivers/ubd_kern.c 2004-10-12 01:52:22.521480664 +0200
@@ -396,14 +396,13 @@ int thread_fd = -1;
*/
int intr_count = 0;
-static void ubd_finish(struct request *req, int error)
+/* 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 +411,17 @@ static void ubd_finish(struct request *r
req->errors = 0;
req->nr_sectors -= nsect;
req->current_nr_sectors = 0;
- spin_lock(&ubd_io_lock);
end_request(req, 1);
+}
+
+static inline void ubd_finish(struct request *req, int error)
+{
+ spin_lock(&ubd_io_lock);
+ __ubd_finish(req, error);
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 @@ static int prepare_mmap_request(struct u
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 @@ static int prepare_request(struct reques
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 @@ static int prepare_request(struct reques
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 @@ static void do_ubd_request(request_queue
err = prepare_request(req, &io_req);
if(!err){
do_io(&io_req);
- ubd_finish(req, io_req.error);
+ __ubd_finish(req, io_req.error);
}
}
}
_