RDMA/siw: Fix a condition race issue in MPA request processing

The calling of siw_cm_upcall and detaching new_cep with its listen_cep
should be atomistic semantics. Otherwise siw_reject may be called in a
temporary state, e,g, siw_cm_upcall is called but the new_cep->listen_cep
has not being cleared.

This fixes a WARN:

  WARNING: CPU: 7 PID: 201 at drivers/infiniband/sw/siw/siw_cm.c:255 siw_cep_put+0x125/0x130 [siw]
  CPU: 2 PID: 201 Comm: kworker/u16:22 Kdump: loaded Tainted: G            E     5.17.0-rc7 #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  Workqueue: iw_cm_wq cm_work_handler [iw_cm]
  RIP: 0010:siw_cep_put+0x125/0x130 [siw]
  Call Trace:
   <TASK>
   siw_reject+0xac/0x180 [siw]
   iw_cm_reject+0x68/0xc0 [iw_cm]
   cm_work_handler+0x59d/0xe20 [iw_cm]
   process_one_work+0x1e2/0x3b0
   worker_thread+0x50/0x3a0
   ? rescuer_thread+0x390/0x390
   kthread+0xe5/0x110
   ? kthread_complete_and_exit+0x20/0x20
   ret_from_fork+0x1f/0x30
   </TASK>

Fixes: 6c52fdc ("rdma/siw: connection management")
Link: https://lore.kernel.org/r/d528d83466c44687f3872eadcb8c184528b2e2d4.1650526554.git.chengyou@linux.alibaba.com
Reported-by: Luis Chamberlain <[email protected]>
Reviewed-by: Bernard Metzler <[email protected]>
Signed-off-by: Cheng Xu <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

drivers/infiniband/sw/siw/siw_cm.c

@@ -968,14 +968,15 @@ static void siw_accept_newconn(struct siw_cep *cep)
 
 		siw_cep_set_inuse(new_cep);
 		rv = siw_proc_mpareq(new_cep);
-		siw_cep_set_free(new_cep);
-
 		if (rv != -EAGAIN) {
 			siw_cep_put(cep);
 			new_cep->listen_cep = NULL;
-			if (rv)
+			if (rv) {
+				siw_cep_set_free(new_cep);
 				goto error;
+			}
 		}
+		siw_cep_set_free(new_cep);
 	}
 	return;