[PATCH] dm thin: reinstate missing mempool_free incell_release_singleton

[Mike Snitzer]

Hi Greg,

3.3-stable pulled in upstream commit
6f94a4c45a6f744383f9f695dde019998db3df55 (dm thin: fix stacked bi_next usage)

But later in the 3.4 development window it was determined that that
commit introduced a significant leak.  The following upstream commit
fixes it (but unfortunately didn't cc: stable).

-------------------

From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit 03aaae7cdc71bc306888440b1f569d463e917b6d upstream.

Fix a significant memory leak inadvertently introduced during
simplification of cell_release_singleton() in commit
6f94a4c45a6f744383f9f695dde019998db3df55 ("dm thin: fix stacked bi_next
usage").

A cell's hlist_del() must be accompanied by a mempool_free().
Use __cell_release() to do this, like before.

Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
---
 drivers/md/dm-thin.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 213ae32..301db0f 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -279,8 +279,10 @@ static void __cell_release(struct cell *cell, struct bio_list *inmates)
 
 	hlist_del(&cell->list);
 
-	bio_list_add(inmates, cell->holder);
-	bio_list_merge(inmates, &cell->bios);
+	if (inmates) {
+		bio_list_add(inmates, cell->holder);
+		bio_list_merge(inmates, &cell->bios);
+	}
 
 	mempool_free(cell, prison->cell_pool);
 }
@@ -303,9 +305,10 @@ static void cell_release(struct cell *cell, struct bio_list *bios)
  */
 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));
+
+	__cell_release(cell, NULL);
 }
 
 static void cell_release_singleton(struct cell *cell, struct bio *bio)
-- 
1.7.4.4
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