RDMA/ib_srp: Fix a deadlock

stable inclusion
from stable-4.19.232
commit d7997d19dfa7001ca41e971cd9efd091bb195b51
category: bugfix
https: https://gitee.com/openeuler/kernel/issues/I5LYLQ
CVE: NA

--------------------------------

[ Upstream commit 081bdc9f ]

Remove the flush_workqueue(system_long_wq) call since flushing
system_long_wq is deadlock-prone and since that call is redundant with a
preceding cancel_work_sync()

Link: https://lore.kernel.org/r/20220215210511.28303-3-bvanassche@acm.org


Fixes: ef6c49d8 ("IB/srp: Eliminate state SRP_TARGET_DEAD")
Reported-by:  <syzbot+831661966588c802aae9@syzkaller.appspotmail.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Luo Meng <luomeng12@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>