On Tue, Dec 16 2014 at 11:00pm -0500,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> From: Keith Busch <keith.busch@xxxxxxxxx>
>
> For blk-mq request-based DM the responsibility of allocating a cloned
> request is transfered from DM core to the target type so that the cloned
> request is allocated from the appropriate request_queue's pool and
> initialized for the target block device. The original request's
> 'special' now points to the dm_rq_target_io because the clone is
> allocated later in the block layer rather than in DM core.
>
> Care was taken to preserve compatibility with old-style block request
> completion that requires request-based DM _not_ acquire the clone
> request's queue lock in the completion path. As such, there are now 2
> different request-based dm_target interfaces:
> 1) the original .map_rq() interface will continue to be used for
> non-blk-mq devices -- the preallocated clone request is passed in
> from DM core.
> 2) a new .clone_and_map_rq() and .release_clone_rq() will be used for
> blk-mq devices -- blk_get_request() and blk_put_request() are used
> respectively from these hooks.
>
> dm_table_set_type() was updated to detect if the request-based target is
> being stacked on blk-mq devices, if so DM_TYPE_MQ_REQUEST_BASED is set.
> DM core disallows switching the DM table's type after it is set. This
> means that there is no mixing of non-blk-mq and blk-mq devices within
> the same request-based DM table.
>
> Signed-off-by: Keith Busch <keith.busch@xxxxxxxxx>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
I did some testing using the DM "error" target and found some error path
fixes were needed, so I folded the following changes into this last
patch and pushed the rebased result to the linux-dm.git
'dm-for-3.20-blk-mq' branch:
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index df408bc..1fa6f14 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -424,6 +424,7 @@ static int __multipath_map(struct dm_target *ti, struct request *clone,
*__clone = blk_get_request(bdev_get_queue(bdev),
rq_data_dir(rq), GFP_KERNEL);
if (IS_ERR(*__clone))
+ /* ENOMEM, requeue */
goto out_unlock;
(*__clone)->cmd_flags |= REQ_FAILFAST_TRANSPORT;
}
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 612e1c1..19914f6 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1044,7 +1044,7 @@ static void free_rq_clone(struct request *clone)
struct dm_rq_target_io *tio = clone->end_io_data;
blk_rq_unprep_clone(clone);
- if (clone->q->mq_ops)
+ if (clone->q && clone->q->mq_ops)
tio->ti->type->release_clone_rq(clone);
else
free_clone_request(tio->md, clone);
@@ -1855,15 +1855,15 @@ static int dm_prep_fn(struct request_queue *q, struct request *rq)
/*
* Returns:
- * 0 : the request has been processed (not requeued)
- * 1 : the request has been requeued
- * < 0 : the original request needs to be requeued
+ * 0 : the request has been processed (not requeued)
+ * 1 : the request has been requeued
+ * DM_MAPIO_REQUEUE : the original request needs to be requeued
*/
static int map_request(struct dm_target *ti, struct request *rq,
struct mapped_device *md)
{
struct request *clone = NULL;
- int r, r2, requeued = 0;
+ int r, requeued = 0;
struct dm_rq_target_io *tio = rq->special;
if (tio->clone) {
@@ -1871,12 +1871,17 @@ static int map_request(struct dm_target *ti, struct request *rq,
r = ti->type->map_rq(ti, clone, &tio->info);
} else {
r = ti->type->clone_and_map_rq(ti, rq, &tio->info, &clone);
+ if (r < 0) {
+ /* The target wants to complete the I/O */
+ dm_kill_unmapped_request(rq, r);
+ return r;
+ }
if (IS_ERR(clone))
- return PTR_ERR(clone);
- r2 = setup_clone(clone, rq, tio, GFP_KERNEL);
- if (r2) {
+ return DM_MAPIO_REQUEUE;
+ if (setup_clone(clone, rq, tio, GFP_KERNEL)) {
+ /* -ENOMEM */
ti->type->release_clone_rq(clone);
- return r2;
+ return DM_MAPIO_REQUEUE;
}
}
@@ -1915,7 +1920,7 @@ static void map_tio_request(struct kthread_work *work)
struct request *rq = tio->orig;
struct mapped_device *md = tio->md;
- if (map_request(tio->ti, rq, md) < 0)
+ if (map_request(tio->ti, rq, md) == DM_MAPIO_REQUEUE)
dm_requeue_unmapped_original_request(md, rq);
}
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