[PATCH v1] xprtrdma: Fix BUG after a device removal

Michal Kalderon reports a BUG that occurs just after device removal:

[  169.112490] rpcrdma: removing device qedr0 for 192.168.110.146:20049
[  169.143909] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
[  169.181837] IP: rpcrdma_dma_unmap_regbuf+0xa/0x60 [rpcrdma]

The RPC/RDMA client transport attempts to allocate some resources
on demand. Registered buffers are one such resource. These are
allocated (or re-allocated) by xprt_rdma_allocate to hold RPC Call
and Reply messages. A hardware resource is associated with each of
these buffers, as they can be used for a Send or Receive Work
Request.

If a device is removed from under an NFS/RDMA mount, the transport
layer is responsible for releasing all hardware resources before
the device can be finally unplugged. A BUG results when the NFS
mount hasn't yet seen much activity: the transport tries to release
resources that haven't yet been allocated.

rpcrdma_free_regbuf() already checks for this case, so just move
that check to cover the DEVICE_REMOVAL case as well.

Reported-by: Michal Kalderon <Michal.Kalderon-YGCgFSpz5w/QT0dZR+AlfA@public.gmane.org>
Fixes: bebd031866ca ("xprtrdma: Support unplugging an HCA ...")
Signed-off-by: Chuck Lever <redacted>
---
 net/sunrpc/xprtrdma/verbs.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index bb56b9d..e6f84a6 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c

@@ -1502,6 +1502,9 @@ struct rpcrdma_regbuf *
 static void
 rpcrdma_dma_unmap_regbuf(struct rpcrdma_regbuf *rb)
 {
+	if (!rb)
+		return;
+
 	if (!rpcrdma_regbuf_is_mapped(rb))
 		return;
 

@@ -1517,9 +1520,6 @@ struct rpcrdma_regbuf *
 void
 rpcrdma_free_regbuf(struct rpcrdma_regbuf *rb)
 {
-	if (!rb)
-		return;
-
 	rpcrdma_dma_unmap_regbuf(rb);
 	kfree(rb);
 }

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