xprtrdma: Fix oops in Receive handler after device removal

Since v5.4, a device removal occasionally triggered this oops:

Dec  2 17:13:53 manet kernel: BUG: unable to handle page fault for address: 0000000c00000219
Dec  2 17:13:53 manet kernel: #PF: supervisor read access in kernel mode
Dec  2 17:13:53 manet kernel: #PF: error_code(0x0000) - not-present page
Dec  2 17:13:53 manet kernel: PGD 0 P4D 0
Dec  2 17:13:53 manet kernel: Oops: 0000 [#1] SMP
Dec  2 17:13:53 manet kernel: CPU: 2 PID: 468 Comm: kworker/2:1H Tainted: G        W         5.4.0-00050-g53717e43af61 #883
Dec  2 17:13:53 manet kernel: Hardware name: Supermicro SYS-6028R-T/X10DRi, BIOS 1.1a 10/16/2015
Dec  2 17:13:53 manet kernel: Workqueue: ib-comp-wq ib_cq_poll_work [ib_core]
Dec  2 17:13:53 manet kernel: RIP: 0010:rpcrdma_wc_receive+0x7c/0xf6 [rpcrdma]
Dec  2 17:13:53 manet kernel: Code: 6d 8b 43 14 89 c1 89 45 78 48 89 4d 40 8b 43 2c 89 45 14 8b 43 20 89 45 18 48 8b 45 20 8b 53 14 48 8b 30 48 8b 40 10 48 8b 38 <48> 8b 87 18 02 00 00 48 85 c0 75 18 48 8b 05 1e 24 c4 e1 48 85 c0
Dec  2 17:13:53 manet kernel: RSP: 0018:ffffc900035dfe00 EFLAGS: 00010246
Dec  2 17:13:53 manet kernel: RAX: ffff888467290000 RBX: ffff88846c638400 RCX: 0000000000000048
Dec  2 17:13:53 manet kernel: RDX: 0000000000000048 RSI: 00000000f942e000 RDI: 0000000c00000001
Dec  2 17:13:53 manet kernel: RBP: ffff888467611b00 R08: ffff888464e4a3c4 R09: 0000000000000000
Dec  2 17:13:53 manet kernel: R10: ffffc900035dfc88 R11: fefefefefefefeff R12: ffff888865af4428
Dec  2 17:13:53 manet kernel: R13: ffff888466023000 R14: ffff88846c63f000 R15: 0000000000000010
Dec  2 17:13:53 manet kernel: FS:  0000000000000000(0000) GS:ffff88846fa80000(0000) knlGS:0000000000000000
Dec  2 17:13:53 manet kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Dec  2 17:13:53 manet kernel: CR2: 0000000c00000219 CR3: 0000000002009002 CR4: 00000000001606e0
Dec  2 17:13:53 manet kernel: Call Trace:
Dec  2 17:13:53 manet kernel: __ib_process_cq+0x5c/0x14e [ib_core]
Dec  2 17:13:53 manet kernel: ib_cq_poll_work+0x26/0x70 [ib_core]
Dec  2 17:13:53 manet kernel: process_one_work+0x19d/0x2cd
Dec  2 17:13:53 manet kernel: ? cancel_delayed_work_sync+0xf/0xf
Dec  2 17:13:53 manet kernel: worker_thread+0x1a6/0x25a
Dec  2 17:13:53 manet kernel: ? cancel_delayed_work_sync+0xf/0xf
Dec  2 17:13:53 manet kernel: kthread+0xf4/0xf9
Dec  2 17:13:53 manet kernel: ? kthread_queue_delayed_work+0x74/0x74
Dec  2 17:13:53 manet kernel: ret_from_fork+0x24/0x30

The proximal cause is that this rpcrdma_rep has a rr_rdmabuf that
is still pointing to the old ib_device, which has been freed. The
only way that is possible is if this rpcrdma_rep was not destroyed
by rpcrdma_ia_remove.

Debugging showed that was indeed the case: this rpcrdma_rep was
still in use by a completing RPC at the time of the device removal,
and thus wasn't on the rep free list. So, it was not found by
rpcrdma_reps_destroy().

The fix is to introduce a list of all rpcrdma_reps so that they all
can be found when a device is removed. That list is used to perform
only regbuf DMA unmapping, replacing that call to
rpcrdma_reps_destroy().

Meanwhile, to prevent corruption of this list, I've moved the
destruction of temp rpcrdma_rep objects to rpcrdma_post_recvs().
rpcrdma_xprt_drain() ensures that post_recvs (and thus rep_destroy) is
not invoked while rpcrdma_reps_unmap is walking rb_all_reps, thus
protecting the rb_all_reps list.

Fixes: b0b227f0 ("xprtrdma: Use an llist to manage free rpcrdma_reps")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/verbs.c

@@ -77,7 +77,7 @@
 static void rpcrdma_sendctx_put_locked(struct rpcrdma_xprt *r_xprt,
 				       struct rpcrdma_sendctx *sc);
 static void rpcrdma_reqs_reset(struct rpcrdma_xprt *r_xprt);
-static void rpcrdma_reps_destroy(struct rpcrdma_buffer *buf);
+static void rpcrdma_reps_unmap(struct rpcrdma_xprt *r_xprt);
 static void rpcrdma_mrs_create(struct rpcrdma_xprt *r_xprt);
 static void rpcrdma_mrs_destroy(struct rpcrdma_xprt *r_xprt);
 static struct rpcrdma_regbuf *
@@ -421,7 +421,7 @@ rpcrdma_ia_remove(struct rpcrdma_ia *ia)
 	/* The ULP is responsible for ensuring all DMA
 	 * mappings and MRs are gone.
 	 */
-	rpcrdma_reps_destroy(buf);
+	rpcrdma_reps_unmap(r_xprt);
 	list_for_each_entry(req, &buf->rb_allreqs, rl_all) {
 		rpcrdma_regbuf_dma_unmap(req->rl_rdmabuf);
 		rpcrdma_regbuf_dma_unmap(req->rl_sendbuf);
@@ -1092,6 +1092,7 @@ static struct rpcrdma_rep *rpcrdma_rep_create(struct rpcrdma_xprt *r_xprt,
 	rep->rr_recv_wr.sg_list = &rep->rr_rdmabuf->rg_iov;
 	rep->rr_recv_wr.num_sge = 1;
 	rep->rr_temp = temp;
+	list_add(&rep->rr_all, &r_xprt->rx_buf.rb_all_reps);
 	return rep;
 
 out_free:
@@ -1102,6 +1103,7 @@ static struct rpcrdma_rep *rpcrdma_rep_create(struct rpcrdma_xprt *r_xprt,
 
 static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep)
 {
+	list_del(&rep->rr_all);
 	rpcrdma_regbuf_free(rep->rr_rdmabuf);
 	kfree(rep);
 }
@@ -1120,10 +1122,16 @@ static struct rpcrdma_rep *rpcrdma_rep_get_locked(struct rpcrdma_buffer *buf)
 static void rpcrdma_rep_put(struct rpcrdma_buffer *buf,
 			    struct rpcrdma_rep *rep)
 {
-	if (!rep->rr_temp)
-		llist_add(&rep->rr_node, &buf->rb_free_reps);
-	else
-		rpcrdma_rep_destroy(rep);
+	llist_add(&rep->rr_node, &buf->rb_free_reps);
+}
+
+static void rpcrdma_reps_unmap(struct rpcrdma_xprt *r_xprt)
+{
+	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
+	struct rpcrdma_rep *rep;
+
+	list_for_each_entry(rep, &buf->rb_all_reps, rr_all)
+		rpcrdma_regbuf_dma_unmap(rep->rr_rdmabuf);
 }
 
 static void rpcrdma_reps_destroy(struct rpcrdma_buffer *buf)
@@ -1154,6 +1162,7 @@ int rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt)
 
 	INIT_LIST_HEAD(&buf->rb_send_bufs);
 	INIT_LIST_HEAD(&buf->rb_allreqs);
+	INIT_LIST_HEAD(&buf->rb_all_reps);
 
 	rc = -ENOMEM;
 	for (i = 0; i < buf->rb_max_requests; i++) {
@@ -1506,6 +1515,10 @@ void rpcrdma_post_recvs(struct rpcrdma_xprt *r_xprt, bool temp)
 	wr = NULL;
 	while (needed) {
 		rep = rpcrdma_rep_get_locked(buf);
+		if (rep && rep->rr_temp) {
+			rpcrdma_rep_destroy(rep);
+			continue;
+		}
 		if (!rep)
 			rep = rpcrdma_rep_create(r_xprt, temp);
 		if (!rep)

net/sunrpc/xprtrdma/xprt_rdma.h

@@ -203,6 +203,7 @@ struct rpcrdma_rep {
 	struct xdr_stream	rr_stream;
 	struct llist_node	rr_node;
 	struct ib_recv_wr	rr_recv_wr;
+	struct list_head	rr_all;
 };
 
 /* To reduce the rate at which a transport invokes ib_post_recv
@@ -368,6 +369,7 @@ struct rpcrdma_buffer {
 
 	struct list_head	rb_allreqs;
 	struct list_head	rb_all_mrs;
+	struct list_head	rb_all_reps;
 
 	struct llist_head	rb_free_reps;