The holder can be passed down to lower devices which may want to use
bi_next themselves. Also added BUG_ON checks to confirm fix.
---
drivers/md/dm-thin.c | 35 ++++++++++++++++++++++-------------
1 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index c308757..6ef03a2 100644
--- a/drivers/md/dm-thin.c
+++ b/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 +220,8 @@ static struct cell *__search_bucket(struct hlist_head *bucket,
* 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,
+ * or < 0 on error.
*/
static int bio_detain(struct bio_prison *prison, struct cell_key *key,
struct bio *inmate, struct cell **ref)
@@ -256,21 +256,25 @@ static int bio_detain(struct bio_prison *prison, struct cell_key *key,

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;
}

@@ -286,6 +290,7 @@ static void __cell_release(struct cell *cell, struct bio_list *inmates)
if (inmates)
bio_list_merge(inmates, &cell->bios);

+ bio_list_add_head(inmates, cell->holder);
mempool_free(cell, prison->cell_pool);
}

@@ -662,8 +667,10 @@ static void remap_and_issue(struct thin_c *tc, struct bio *bio,
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);
+ }
}

/*
@@ -1302,8 +1309,10 @@ static void process_deferred_bios(struct pool *pool)
return;
}

- while ((bio = bio_list_pop(&bios)))
+ while ((bio = bio_list_pop(&bios))) {
+ BUG_ON(bio->bi_next);
generic_make_request(bio);
+ }
}

static void do_worker(struct work_struct *ws)
--
1.7.5.4

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