dm cache: fix flushing uninitialized delayed_work on cache_ctr error

In the Linux kernel, the following vulnerability has been resolved:

dm cache: fix flushing uninitialized delayed_work on cache_ctr error

An unexpected WARN_ON from flush_work() may occur when cache creation

fails, caused by destroying the uninitialized delayed_work waker in the

error path of cache_create(). For example, the warning appears on the

superblock checksum error.

Reproduce steps:

dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"

dmsetup create cdata --table "0 65536 linear /dev/sdc 8192"

dmsetup create corig --table "0 524288 linear /dev/sdc 262144"

dd if=/dev/urandom of=/dev/mapper/cmeta bs=4k count=1 oflag=direct

dmsetup create cache --table "0 524288 cache /dev/mapper/cmeta \

/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"

Kernel logs:

(snip)

WARNING: CPU: 0 PID: 84 at kernel/workqueue.c:4178 __flush_work+0x5d4/0x890

Fix by pulling out the cancel_delayed_work_sync() from the constructor's

error path. This patch doesn't affect the use-after-free fix for

concurrent dm_resume and dm_destroy (commit 6a459d8edbdb ("dm cache: Fix

UAF in destroy()")) as cache_dtr is not changed.