[added to the 4.1 stable tree] bcache: fix cache_set_flush() NULL pointer dereference on OOM

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From: Eric Wheeler <git@xxxxxxxxxxxxxxxxxx>

This patch has been added to the 4.1 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit f8b11260a445169989d01df75d35af0f56178f95 ]

When bch_cache_set_alloc() fails to kzalloc the cache_set, the
asyncronous closure handling tries to dereference a cache_set that
hadn't yet been allocated inside of cache_set_flush() which is called
by __cache_set_unregister() during cleanup.  This appears to happen only
during an OOM condition on bcache_register.

Signed-off-by: Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
 drivers/md/bcache/super.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 2d0650de..2a10283 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1404,6 +1404,9 @@ static void cache_set_flush(struct closure *cl)
 	struct btree *b;
 	unsigned i;
 
+	if (!c)
+		closure_return(cl);
+
 	bch_cache_accounting_destroy(&c->accounting);
 
 	kobject_put(&c->internal);
-- 
2.5.0

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