RDMA/ib_srp: Fix a deadlock

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/[e-mail]
Fixes: ef6c49d87c34 ("IB/srp: Eliminate state SRP_TARGET_DEAD")
Reported-by: [e-mail]
Signed-off-by: Bart Van Assche <[e-mail]>
Reviewed-by: Leon Romanovsky <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/infiniband/ulp/srp/ib_srp.c

···
 		spin_unlock(&host->target_lock);
 
 		/*
-		 * Wait for tl_err and target port removal tasks.
+		 * srp_queue_remove_work() queues a call to
+		 * srp_remove_target(). The latter function cancels
+		 * target->tl_err_work so waiting for the remove works to
+		 * finish is sufficient.
 		 */
-		flush_workqueue(system_long_wq);
 		flush_workqueue(srp_remove_wq);
 
 		kfree(host);