scsi: hisi_sas: Replace in_softirq() check in hisi_sas_task_exec()

For IOs from upper layer, preemption may be disabled as it may be called by
function __blk_mq_delay_run_hw_queue which will call get_cpu() (it disables
preemption). So if flags HISI_SAS_REJECT_CMD_BIT is set in function
hisi_sas_task_exec(), it may disable preempt twice after down() and up()
which will cause following call trace:

BUG: scheduling while atomic: fio/60373/0x00000002
Call trace:
dump_backtrace+0x0/0x150
show_stack+0x24/0x30
dump_stack+0xa0/0xc4
__schedule_bug+0x68/0x88
__schedule+0x4b8/0x548
schedule+0x40/0xd0
schedule_timeout+0x200/0x378
__down+0x78/0xc8
down+0x54/0x70
hisi_sas_task_exec.isra.10+0x598/0x8d8 [hisi_sas_main]
hisi_sas_queue_command+0x28/0x38 [hisi_sas_main]
sas_queuecommand+0x168/0x1b0 [libsas]
scsi_queue_rq+0x2ac/0x980
blk_mq_dispatch_rq_list+0xb0/0x550
blk_mq_do_dispatch_sched+0x6c/0x110
blk_mq_sched_dispatch_requests+0x114/0x1d8
__blk_mq_run_hw_queue+0xb8/0x130
__blk_mq_delay_run_hw_queue+0x1c0/0x220
blk_mq_run_hw_queue+0xb0/0x128
blk_mq_sched_insert_requests+0xdc/0x208
blk_mq_flush_plug_list+0x1b4/0x3a0
blk_flush_plug_list+0xdc/0x110
blk_finish_plug+0x3c/0x50
blkdev_direct_IO+0x404/0x550
generic_file_read_iter+0x9c/0x848
blkdev_read_iter+0x50/0x78
aio_read+0xc8/0x170
io_submit_one+0x1fc/0x8d8
__arm64_sys_io_submit+0xdc/0x280
el0_svc_common.constprop.0+0xe0/0x1e0
el0_svc_handler+0x34/0x90
el0_svc+0x10/0x14
...

To solve the issue, check preemptible() to avoid disabling preempt multiple
when flag HISI_SAS_REJECT_CMD_BIT is set.

Link: https://lore.kernel.org/r/1571926105-74636-5-git-send-email-john.garry@huawei.comSigned-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hisi_sas/hisi_sas_main.c

@@ -587,7 +587,13 @@ static int hisi_sas_task_exec(struct sas_task *task, gfp_t gfp_flags,
 	dev = hisi_hba->dev;
 
 	if (unlikely(test_bit(HISI_SAS_REJECT_CMD_BIT, &hisi_hba->flags))) {
-		if (in_softirq())
+		/*
+		 * For IOs from upper layer, it may already disable preempt
+		 * in the IO path, if disable preempt again in down(),
+		 * function schedule() will report schedule_bug(), so check
+		 * preemptible() before goto down().
+		 */
+		if (!preemptible())
 			return -EINVAL;
 
 		down(&hisi_hba->sem);