blk-mq: flush pending hctx->run_work before freeing hctx

blk-mq: flush pending hctx->run_work before freeing hctx

During resume block driver starts the queues and add hctx->run_work to wq
to process the pending request in hardware queue. In the same sequence
block driver frees the hw queues if respective mapped CPU is offline.
If the hctx->run_work schedules afterwards, kernel crashes because hctx
is freed. To fix the issue flush hctx->run_work before freeing hctx.

Unable to handle kernel NULL pointer dereference at virtual address 00000000
Mem abort info:
  ESR = 0x96000005
  Exception class = DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
Data abort info:
  ISV = 0, ISS = 0x00000005
  CM = 0, WnR = 0
user pgtable: 4k pages, 39-bit VAs, pgd = ffffffc364390000
[0000000000000000] *pgd=0000000000000000, *pud=0000000000000000
Internal error: Oops: 96000005 [#1] PREEMPT SMP
CPU: 1 PID: 49 Comm: kworker/6:0H Tainted: G         C      4.9.132-tegra-g8cc25a4-dirty #9
Hardware name: galen (DT)
Workqueue: kblockd blk_mq_run_work_fn
task: ffffffc3ecc08d40 task.stack: ffffffc3ecc14000
PC is at __blk_mq_run_hw_queue+0xfc/0x858
LR is at __blk_mq_run_hw_queue+0x618/0x858
pc : [<ffffff80087b565c>] lr : [<ffffff80087b5b78>] pstate: 80c00045
sp : ffffffc3ecc17c00
x29: ffffffc3ecc17c00 x28: ffffffc3ecc17cc8
x27: 0000000000000000 x26: 0000000000000000
x25: 0000000000000000 x24: ffffffc3d4088000
x23: 0000000000000000 x22: ffffffc3ecc17cb8
x21: ffffffc3d3843090 x20: ffffffc3d3843000
x19: 0000000000000000 x18: ffffff800a7d7450
x17: 0000000000000000 x16: 0000000000000002
x15: ffffff800a7d7468 x14: 3d3d3d3d3d3d3d3d
x13: 3d3d3d3d3d3d3d3d x12: 3d3d3d3d3d3d3d3d
x11: 3d3d3d3d3d3d3d3d x10: 3d3d3d3d3d3d3d3d
x9 : 3d3d3d3d3d3d3d3d x8 : ffffffc3ffc53838
x7 : 0000000000000000 x6 : ffffffc3ffc53838
x5 : 0000000000000000 x4 : 0000000000000001
x3 : 0000000000000050 x2 : 0000000000000000
x1 : 0000000000040984 x0 : 0000000000000000

Process kworker/6:0H (pid: 49, stack limit = 0xffffffc3ecc14028)
Call trace:
[<ffffff80087b565c>] __blk_mq_run_hw_queue+0xfc/0x858
[<ffffff80087b5e18>] blk_mq_run_work_fn+0x20/0x30
[<ffffff8008105398>] process_one_work+0x1d8/0xb30
[<ffffff8008105e78>] worker_thread+0x188/0x790
[<ffffff800811119c>] kthread+0x12c/0x200
[<ffffff80080837d0>] ret_from_fork+0x10/0x40

bug 200456501

Change-Id: Iecf16bb18daa514bb6700080e3ff7951a9c5126a
Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1926876
GVS: Gerrit_Virtual_Submit
Reviewed-by: Vidya Sagar <vidyas@nvidia.com>
Reviewed-by: Ashutosh Jha <ajha@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>