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dm: do not initialise full request queue when bio based

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Change bio-based mapped devices no longer to have a fully initialized
request_queue (request_fn, elevator, etc).  This means bio-based DM
devices no longer register elevator sysfs attributes ('iosched/' tree
or 'scheduler' other than "none").

In contrast, a request-based DM device will continue to have a full
request_queue and will register elevator sysfs attributes.  Therefore
a user can determine a DM device's type by checking if elevator sysfs
attributes exist.

First allocate a minimalist request_queue structure for a DM device
(needed for both bio and request-based DM).

Initialization of a full request_queue is deferred until it is known
that the DM device is request-based, at the end of the table load
sequence.

Factor DM device's request_queue initialization:
- common to both request-based and bio-based into dm_init_md_queue().
- specific to request-based into dm_init_request_based_queue().

The md->type_lock mutex is used to protect md->queue, in addition to
md->type, during table_load().

A DM device's first table_load will establish the immutable md->type.
But md->queue initialization, based on md->type, may fail at that time
(because blk_init_allocated_queue cannot allocate memory).  Therefore
any subsequent table_load must (re)try dm_setup_md_queue independently of
establishing md->type.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mike Snitzer 2010-08-12 04:14:02 +01:00 committed by Alasdair G Kergon
parent a5664dad7e
commit 4a0b4ddf26
3 changed files with 79 additions and 26 deletions
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11
drivers/md/dm-ioctl.c
View File

@ -1189,7 +1189,7 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
goto out;
}
/* Protect md->type against concurrent table loads. */
/* Protect md->type and md->queue against concurrent table loads. */
dm_lock_md_type(md);
if (dm_get_md_type(md) == DM_TYPE_NONE)
/* Initial table load: acquire type of table. */
@ -1201,6 +1201,15 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
r = -EINVAL;
goto out;
}
/* setup md->queue to reflect md's type (may block) */
r = dm_setup_md_queue(md);
if (r) {
DMWARN("unable to set up device queue for new table.");
dm_table_destroy(t);
dm_unlock_md_type(md);
goto out;
}
dm_unlock_md_type(md);
/* stage inactive table */

92
drivers/md/dm.c
View File

@ -126,7 +126,7 @@ struct mapped_device {
struct request_queue *queue;
unsigned type;
/* Protect type against concurrent access. */
/* Protect queue and type against concurrent access. */
struct mutex type_lock;
struct gendisk *disk;
@ -1856,6 +1856,28 @@ static const struct block_device_operations dm_blk_dops;
static void dm_wq_work(struct work_struct *work);
static void dm_rq_barrier_work(struct work_struct *work);
static void dm_init_md_queue(struct mapped_device *md)
{
/*
* Request-based dm devices cannot be stacked on top of bio-based dm
* devices. The type of this dm device has not been decided yet.
* The type is decided at the first table loading time.
* To prevent problematic device stacking, clear the queue flag
* for request stacking support until then.
*
* This queue is new, so no concurrency on the queue_flags.
*/
queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
md->queue->queuedata = md;
md->queue->backing_dev_info.congested_fn = dm_any_congested;
md->queue->backing_dev_info.congested_data = md;
blk_queue_make_request(md->queue, dm_request);
blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
md->queue->unplug_fn = dm_unplug_all;
blk_queue_merge_bvec(md->queue, dm_merge_bvec);
}
/*
* Allocate and initialise a blank device with a given minor.
*/
@ -1895,33 +1917,11 @@ static struct mapped_device *alloc_dev(int minor)
INIT_LIST_HEAD(&md->uevent_list);
spin_lock_init(&md->uevent_lock);
md->queue = blk_init_queue(dm_request_fn, NULL);
md->queue = blk_alloc_queue(GFP_KERNEL);
if (!md->queue)
goto bad_queue;
/*
* Request-based dm devices cannot be stacked on top of bio-based dm
* devices. The type of this dm device has not been decided yet,
* although we initialized the queue using blk_init_queue().
* The type is decided at the first table loading time.
* To prevent problematic device stacking, clear the queue flag
* for request stacking support until then.
*
* This queue is new, so no concurrency on the queue_flags.
*/
queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
md->saved_make_request_fn = md->queue->make_request_fn;
md->queue->queuedata = md;
md->queue->backing_dev_info.congested_fn = dm_any_congested;
md->queue->backing_dev_info.congested_data = md;
blk_queue_make_request(md->queue, dm_request);
blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
md->queue->unplug_fn = dm_unplug_all;
blk_queue_merge_bvec(md->queue, dm_merge_bvec);
blk_queue_softirq_done(md->queue, dm_softirq_done);
blk_queue_prep_rq(md->queue, dm_prep_fn);
blk_queue_lld_busy(md->queue, dm_lld_busy);
blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH);
dm_init_md_queue(md);
md->disk = alloc_disk(1);
if (!md->disk)
@ -2160,6 +2160,48 @@ unsigned dm_get_md_type(struct mapped_device *md)
return md->type;
}
/*
* Fully initialize a request-based queue (->elevator, ->request_fn, etc).
*/
static int dm_init_request_based_queue(struct mapped_device *md)
{
struct request_queue *q = NULL;
if (md->queue->elevator)
return 1;
/* Fully initialize the queue */
q = blk_init_allocated_queue(md->queue, dm_request_fn, NULL);
if (!q)
return 0;
md->queue = q;
md->saved_make_request_fn = md->queue->make_request_fn;
dm_init_md_queue(md);
blk_queue_softirq_done(md->queue, dm_softirq_done);
blk_queue_prep_rq(md->queue, dm_prep_fn);
blk_queue_lld_busy(md->queue, dm_lld_busy);
blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH);
elv_register_queue(md->queue);
return 1;
}
/*
* Setup the DM device's queue based on md's type
*/
int dm_setup_md_queue(struct mapped_device *md)
{
if ((dm_get_md_type(md) == DM_TYPE_REQUEST_BASED) &&
!dm_init_request_based_queue(md)) {
DMWARN("Cannot initialize queue for request-based mapped device");
return -EINVAL;
}
return 0;
}
static struct mapped_device *dm_find_md(dev_t dev)
{
struct mapped_device *md;

2
drivers/md/dm.h
View File

@ -71,6 +71,8 @@ void dm_unlock_md_type(struct mapped_device *md);
void dm_set_md_type(struct mapped_device *md, unsigned type);
unsigned dm_get_md_type(struct mapped_device *md);
int dm_setup_md_queue(struct mapped_device *md);
/*
* To check the return value from dm_table_find_target().
*/