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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 02-10-2012, 05:03 PM
Mike Snitzer
 
Default dm thin: don't use the bi_next field for the holder of a cell

From: Joe Thornber <ejt@redhat.com>

The holder can be passed down to lower devices which may want to use
bi_next themselves. Also add BUG_ON check to confirm fix.

When releasing bios that have been detained in a cell, fix the order in
which the holder and other cellmates are added to the inmates list:
append holder first followed by the other cellmates.

Clarify what is expected during each cell release by introducing
variants of __cell_release.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
drivers/md/dm-thin.c | 86 ++++++++++++++++++++++++++++++++-------------------
1 file changed, 54 insertions(+), 32 deletions(-)

Index: linux-2.6/drivers/md/dm-thin.c
================================================== =================
--- linux-2.6.orig/drivers/md/dm-thin.c
+++ linux-2.6/drivers/md/dm-thin.c
@@ -124,7 +124,7 @@ struct cell {
struct hlist_node list;
struct bio_prison *prison;
struct cell_key key;
- unsigned count;
+ struct bio *holder;
struct bio_list bios;
};

@@ -220,8 +220,7 @@ static struct cell *__search_bucket(stru
* This may block if a new cell needs allocating. You must ensure that
* cells will be unlocked even if the calling thread is blocked.
*
- * Returns the number of entries in the cell prior to the new addition
- * or < 0 on failure.
+ * Returns 1 if the cell was already held, 0 if @inmate is the new holder.
*/
static int bio_detain(struct bio_prison *prison, struct cell_key *key,
struct bio *inmate, struct cell **ref)
@@ -235,7 +234,6 @@ static int bio_detain(struct bio_prison

spin_lock_irqsave(&prison->lock, flags);
cell = __search_bucket(prison->cells + hash, key);
-
if (!cell) {
/*
* Allocate a new cell
@@ -249,28 +247,30 @@ static int bio_detain(struct bio_prison
* nobody else has inserted this cell in the meantime.
*/
cell = __search_bucket(prison->cells + hash, key);
-
if (!cell) {
cell = cell2;
cell2 = NULL;

cell->prison = prison;
memcpy(&cell->key, key, sizeof(cell->key));
- cell->count = 0;
+ cell->holder = inmate;
bio_list_init(&cell->bios);
hlist_add_head(&cell->list, prison->cells + hash);
+ r = 0;
+ } else {
+ mempool_free(cell2, prison->cell_pool);
+ cell2 = NULL;
+ r = 1;
+ bio_list_add(&cell->bios, inmate);
}
- }

- r = cell->count++;
- bio_list_add(&cell->bios, inmate);
+ } else {
+ r = 1;
+ bio_list_add(&cell->bios, inmate);
+ }
spin_unlock_irqrestore(&prison->lock, flags);

- if (cell2)
- mempool_free(cell2, prison->cell_pool);
-
*ref = cell;
-
return r;
}

@@ -283,8 +283,10 @@ static void __cell_release(struct cell *

hlist_del(&cell->list);

- if (inmates)
+ if (inmates) {
+ bio_list_add(inmates, cell->holder);
bio_list_merge(inmates, &cell->bios);
+ }

mempool_free(cell, prison->cell_pool);
}
@@ -305,22 +307,45 @@ static void cell_release(struct cell *ce
* bio may be in the cell. This function releases the cell, and also does
* a sanity check.
*/
+static void __cell_release_singleton(struct cell *cell, struct bio *bio)
+{
+ hlist_del(&cell->list);
+ BUG_ON(cell->holder != bio);
+ BUG_ON(!bio_list_empty(&cell->bios));
+}
+
static void cell_release_singleton(struct cell *cell, struct bio *bio)
{
- struct bio_prison *prison = cell->prison;
- struct bio_list bios;
- struct bio *b;
unsigned long flags;
-
- bio_list_init(&bios);
+ struct bio_prison *prison = cell->prison;

spin_lock_irqsave(&prison->lock, flags);
- __cell_release(cell, &bios);
+ __cell_release_singleton(cell, bio);
spin_unlock_irqrestore(&prison->lock, flags);
+}

- b = bio_list_pop(&bios);
- BUG_ON(b != bio);
- BUG_ON(!bio_list_empty(&bios));
+/*
+ * Sometimes we don't want the holder, just the additional bios.
+ */
+static void __cell_release_no_holder(struct cell *cell, struct bio_list *inmates)
+{
+ struct bio_prison *prison = cell->prison;
+
+ hlist_del(&cell->list);
+ if (inmates)
+ bio_list_merge(inmates, &cell->bios);
+
+ mempool_free(cell, prison->cell_pool);
+}
+
+static void cell_release_no_holder(struct cell *cell, struct bio_list *inmates)
+{
+ unsigned long flags;
+ struct bio_prison *prison = cell->prison;
+
+ spin_lock_irqsave(&prison->lock, flags);
+ __cell_release_no_holder(cell, inmates);
+ spin_unlock_irqrestore(&prison->lock, flags);
}

static void cell_error(struct cell *cell)
@@ -662,8 +687,10 @@ static void remap_and_issue(struct thin_
spin_lock_irqsave(&pool->lock, flags);
bio_list_add(&pool->deferred_flush_bios, bio);
spin_unlock_irqrestore(&pool->lock, flags);
- } else
+ } else {
+ BUG_ON(bio->bi_next);
generic_make_request(bio);
+ }
}

/*
@@ -800,21 +827,16 @@ static void cell_defer(struct thin_c *tc
* Same as cell_defer above, except it omits one particular detainee,
* a write bio that covers the block and has already been processed.
*/
-static void cell_defer_except(struct thin_c *tc, struct cell *cell,
- struct bio *exception)
+static void cell_defer_except(struct thin_c *tc, struct cell *cell)
{
struct bio_list bios;
- struct bio *bio;
struct pool *pool = tc->pool;
unsigned long flags;

bio_list_init(&bios);
- cell_release(cell, &bios);

spin_lock_irqsave(&pool->lock, flags);
- while ((bio = bio_list_pop(&bios)))
- if (bio != exception)
- bio_list_add(&pool->deferred_bios, bio);
+ cell_release_no_holder(cell, &pool->deferred_bios);
spin_unlock_irqrestore(&pool->lock, flags);

wake_worker(pool);
@@ -854,7 +876,7 @@ static void process_prepared_mapping(str
* the bios in the cell.
*/
if (bio) {
- cell_defer_except(tc, m->cell, bio);
+ cell_defer_except(tc, m->cell);
bio_endio(bio, 0);
} else
cell_defer(tc, m->cell, m->data_block);

--
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