[RFC PATCH 1/8] rqbased-dm: allow blk_get_request() to be called from interrupt context

Kiyoshi Ueda
2006-12-19T22:11:34Z

Currently, blk_get_request() is not ready for being called from
interrupt context because it enables interrupt forcibly in it.

Request-based device-mapper sometimes needs to get a request
in interrupt context to create a clone.
Calling blk_get_request() from interrupt context should be OK
because blk_get_request() returns NULL without sleep if no memory
unless __GFP_WAIT mask is specified, and then the interrupt context
can plug queue to retry after and return immediately.

So this patch allows blk_get_request() to be called from interrupt
context by save/restore current state of irq.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>

diff -rupN 2.6.19.1/block/ll_rw_blk.c 1-blk-get-request-irqrestore/block/ll_rw_blk.c
--- 2.6.19.1/block/ll_rw_blk.c 2006-12-11 14:32:53.000000000 -0500
+++ 1-blk-get-request-irqrestore/block/ll_rw_blk.c 2006-12-15 10:21:29.000000000 -0500
@@ -2064,9 +2064,10 @@ static void freed_request(request_queue_
* Get a free request, queue_lock must be held.
* Returns NULL on failure, with queue_lock held.
* Returns !NULL on success, with queue_lock *not held*.
+ * If flags is given, the irq state is kept when unlocking the queue_lock.
*/
static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
- gfp_t gfp_mask)
+ gfp_t gfp_mask, unsigned long *flags)
{
struct request *rq = NULL;
struct request_list *rl = &q->rq;
@@ -2119,7 +2120,10 @@ static struct request *get_request(reque
if (priv)
rl->elvpriv++;

- spin_unlock_irq(q->queue_lock);
+ if (flags)
+ spin_unlock_irqrestore(q->queue_lock, *flags);
+ else
+ spin_unlock_irq(q->queue_lock);

rq = blk_alloc_request(q, rw, priv, gfp_mask);
if (unlikely(!rq)) {
@@ -2130,7 +2134,10 @@ static struct request *get_request(reque
* Allocating task should really be put onto the front of the
* wait queue, but this is pretty rare.
*/
- spin_lock_irq(q->queue_lock);
+ if (flags)
+ spin_lock_irqsave(q->queue_lock, *flags);
+ else
+ spin_lock_irq(q->queue_lock);
freed_request(q, rw, priv);

/*
@@ -2174,7 +2181,7 @@ static struct request *get_request_wait(
{
struct request *rq;

- rq = get_request(q, rw, bio, GFP_NOIO);
+ rq = get_request(q, rw, bio, GFP_NOIO, NULL);
while (!rq) {
DEFINE_WAIT(wait);
struct request_list *rl = &q->rq;
@@ -2182,7 +2189,7 @@ static struct request *get_request_wait(
prepare_to_wait_exclusive(&rl->wait[rw], &wait,
TASK_UNINTERRUPTIBLE);

- rq = get_request(q, rw, bio, GFP_NOIO);
+ rq = get_request(q, rw, bio, GFP_NOIO, NULL);

if (!rq) {
struct io_context *ioc;
@@ -2213,16 +2220,17 @@ static struct request *get_request_wait(
struct request *blk_get_request(request_queue_t *q, int rw, gfp_t gfp_mask)
{
struct request *rq;
+ unsigned long flags;

BUG_ON(rw != READ && rw != WRITE);

- spin_lock_irq(q->queue_lock);
+ spin_lock_irqsave(q->queue_lock, flags);
if (gfp_mask & __GFP_WAIT) {
rq = get_request_wait(q, rw, NULL);
} else {
- rq = get_request(q, rw, NULL, gfp_mask);
+ rq = get_request(q, rw, NULL, gfp_mask, &flags);
if (!rq)
- spin_unlock_irq(q->queue_lock);
+ spin_unlock_irqrestore(q->queue_lock, flags);
}
/* q->queue_lock is unlocked at this point */