FROMLIST: scsi: ufs: Fix deadlock issue in ufshcd_wait_for_doorbell_clr()

Call shost_for_each_device() with holding host->host_lock will cause
a deadlock situation, which will cause the system to stall (the log
as follow). Fix this issue by using __shost_for_each_device() in
ufshcd_pending_cmds().

stalls on CPUs/tasks:
all trace:
__switch_to+0x120/0x170
0xffff800011643998
ask dump for CPU 5:
ask:kworker/u16:2   state:R  running task     stack:    0 pid:   80 ppid:     2 flags:0x0000000a
orkqueue: events_unbound async_run_entry_fn
all trace:
__switch_to+0x120/0x170
0x0
ask dump for CPU 6:
ask:kworker/u16:6   state:R  running task     stack:    0 pid:  164 ppid:     2 flags:0x0000000a
orkqueue: events_unbound async_run_entry_fn
all trace:
__switch_to+0x120/0x170
0xffff54e7c4429f80
ask dump for CPU 7:
ask:kworker/u16:4   state:R  running task     stack:    0 pid:  153 ppid:     2 flags:0x0000000a
orkqueue: events_unbound async_run_entry_fn
all trace:
__switch_to+0x120/0x170
blk_mq_run_hw_queue+0x34/0x110
blk_mq_sched_insert_request+0xb0/0x120
blk_execute_rq_nowait+0x68/0x88
blk_execute_rq+0x4c/0xd8
__scsi_execute+0xec/0x1d0
scsi_vpd_inquiry+0x84/0xf0
scsi_get_vpd_buf+0x34/0xb8
scsi_attach_vpd+0x34/0x140
scsi_probe_and_add_lun+0xa6c/0xab8
__scsi_scan_target+0x438/0x4f8
scsi_scan_channel+0x6c/0xa8
scsi_scan_host_selected+0xf0/0x150
do_scsi_scan_host+0x88/0x90
scsi_scan_host+0x1b4/0x1d0
ufshcd_async_scan+0x248/0x310
async_run_entry_fn+0x30/0x178
process_one_work+0x1e8/0x368
worker_thread+0x40/0x478
kthread+0x174/0x180
ret_from_fork+0x10/0x20

Fixes: 198b86493c ("BACKPORT: FROMGIT: scsi: ufs: Optimize the command queueing code")
Reported-by: YongQin Liu <yongqin.liu@linaro.org>
Reported-by: Amit Pundir <amit.pundir@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Bean Huo <beanhuo@micron.com>
[ bvanassche: modified "Fixes" tag ]
Link: https://lore.kernel.org/linux-scsi/20211214120537.531628-1-huobean@gmail.com/T/#u
Change-Id: I13a9b9aef63a499323ff5652314ab174f81e987e
Signed-off-by: Bart Van Assche <bvanassche@google.com>

drivers/scsi/ufs/ufshcd.c

@@ -1100,7 +1100,8 @@ static u32 ufshcd_pending_cmds(struct ufs_hba *hba)
 	struct scsi_device *sdev;
 	u32 pending = 0;
 
-	shost_for_each_device(sdev, hba->host)
+	lockdep_assert_held(hba->host->host_lock);
+	__shost_for_each_device(sdev, hba->host)
 		pending += atomic_read(&sdev->device_busy);
 
 	return pending;