[ 094/221] dm thin: replace dm_cell_release_singleton with cell_defer_except

Greg Kroah-Hartman
2013-01-15T22:31:17Z

From: Joe Thornber <ejt@redhat.com>

commit b7ca9c9273e5eebd63880dd8a6e4e5c18fc7901d upstream.

Change existing users of the function dm_cell_release_singleton to share
cell_defer_except instead, and then remove the now-unused function.

Everywhere that calls dm_cell_release_singleton, the bio in question
is the holder of the cell.

If there are no non-holder entries in the cell then cell_defer_except
behaves exactly like dm_cell_release_singleton. Conversely, if there
*are* non-holder entries then dm_cell_release_singleton must not be used
because those entries would need to be deferred.

Consequently, it is safe to replace use of dm_cell_release_singleton
with cell_defer_except.

This patch is a pre-requisite for "dm thin: fix race between
simultaneous io and discards to same block".

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/dm-bio-prison.c | 25 -------------------------
drivers/md/dm-bio-prison.h | 1 -
drivers/md/dm-thin.c | 25 ++++++++++++-------------
3 files changed, 12 insertions(+), 39 deletions(-)

--- a/drivers/md/dm-bio-prison.c
+++ b/drivers/md/dm-bio-prison.c
@@ -208,31 +208,6 @@ void dm_cell_release(struct dm_bio_priso
EXPORT_SYMBOL_GPL(dm_cell_release);

/*
- * There are a couple of places where we put a bio into a cell briefly
- * before taking it out again. In these situations we know that no other
- * bio may be in the cell. This function releases the cell, and also does
- * a sanity check.
- */
-static void __cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
-{
- BUG_ON(cell->holder != bio);
- BUG_ON(!bio_list_empty(&cell->bios));
-
- __cell_release(cell, NULL);
-}
-
-void dm_cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
-{
- unsigned long flags;
- struct dm_bio_prison *prison = cell->prison;
-
- spin_lock_irqsave(&prison->lock, flags);
- __cell_release_singleton(cell, bio);
- spin_unlock_irqrestore(&prison->lock, flags);
-}
-EXPORT_SYMBOL_GPL(dm_cell_release_singleton);
-
-/*
* Sometimes we don't want the holder, just the additional bios.
*/
static void __cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
--- a/drivers/md/dm-bio-prison.h
+++ b/drivers/md/dm-bio-prison.h
@@ -44,7 +44,6 @@ int dm_bio_detain(struct dm_bio_prison *
struct bio *inmate, struct dm_bio_prison_cell **ref);

void dm_cell_release(struct dm_bio_prison_cell *cell, struct bio_list *bios);
-void dm_cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio); // FIXME: bio arg not needed
void dm_cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates);
void dm_cell_error(struct dm_bio_prison_cell *cell);

--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -513,8 +513,7 @@ 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.
+ * Same as cell_defer except it omits the original holder of the cell.
*/
static void cell_defer_except(struct thin_c *tc, struct dm_bio_prison_cell *cell)
{
@@ -936,7 +935,7 @@ static void process_discard(struct thin_
*/
build_data_key(tc->td, lookup_result.block, &key2);
if (dm_bio_detain(tc->pool->prison, &key2, bio, &cell2)) {
- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);
break;
}

@@ -967,8 +966,8 @@ static void process_discard(struct thin_
* a block boundary. So we submit the discard of a
* partial block appropriately.
*/
- dm_cell_release_singleton(cell, bio);
- dm_cell_release_singleton(cell2, bio);
+ cell_defer_except(tc, cell);
+ cell_defer_except(tc, cell2);
if ((!lookup_result.shared) && pool->pf.discard_passdown)
remap_and_issue(tc, bio, lookup_result.block);
else
@@ -980,13 +979,13 @@ static void process_discard(struct thin_
/*
* It isn't provisioned, just forget it.
*/
- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);
bio_endio(bio, 0);
break;

default:
DMERR("discard: find block unexpectedly returned %d", r);
- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);
bio_io_error(bio);
break;
}
@@ -1041,7 +1040,7 @@ static void process_shared_bio(struct th

h->shared_read_entry = dm_deferred_entry_inc(pool->shared_read_ds);

- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);
remap_and_issue(tc, bio, lookup_result->block);
}
}
@@ -1056,7 +1055,7 @@ static void provision_block(struct thin_
* Remap empty bios (flushes) immediately, without provisioning.
*/
if (!bio->bi_size) {
- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);
remap_and_issue(tc, bio, 0);
return;
}
@@ -1066,7 +1065,7 @@ static void provision_block(struct thin_
*/
if (bio_data_dir(bio) == READ) {
zero_fill_bio(bio);
- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);
bio_endio(bio, 0);
return;
}
@@ -1120,7 +1119,7 @@ static void process_bio(struct thin_c *t
* TODO: this will probably have to change when discard goes
* back in.
*/
- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);

if (lookup_result.shared)
process_shared_bio(tc, bio, block, &lookup_result);
@@ -1130,7 +1129,7 @@ static void process_bio(struct thin_c *t

case -ENODATA:
if (bio_data_dir(bio) == READ && tc->origin_dev) {
- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);
remap_to_origin_and_issue(tc, bio);
} else
provision_block(tc, bio, block, cell);
@@ -1138,7 +1137,7 @@ static void process_bio(struct thin_c *t

default:
DMERR("dm_thin_find_block() failed, error = %d", r);
- dm_cell_release_singleton(cell, bio);
+ cell_defer_except(tc, cell);
bio_io_error(bio);
break;
}