xprtrdma: Fix BUG after a device removal

Web:        https://git.kernel.org/torvalds/c/e89e8d8fcdc6751e86ccad794b052fe67e6ad619
Commit:     e89e8d8fcdc6751e86ccad794b052fe67e6ad619
Parent:     1179e2c27efe21167ec9d882b14becefba2ee990
Refname:    refs/heads/master
Author:     Chuck Lever <[email protected]>
AuthorDate: Wed Jan 31 12:34:13 2018 -0500
Committer:  Anna Schumaker <[email protected]>
CommitDate: Fri Feb 2 13:31:04 2018 -0500

    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 <[email protected]>
    Fixes: bebd031866ca ("xprtrdma: Support unplugging an HCA ...")
    Signed-off-by: Chuck Lever <[email protected]>
    Tested-by: Michal Kalderon <[email protected]>
    Cc: [email protected] # v4.12+
    Signed-off-by: Anna Schumaker <[email protected]>
---
 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 bb56b9d849c4..e6f84a6434a0 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1502,6 +1502,9 @@ __rpcrdma_dma_map_regbuf(struct rpcrdma_ia *ia, struct rpcrdma_regbuf *rb)
 static void
 rpcrdma_dma_unmap_regbuf(struct rpcrdma_regbuf *rb)
 {
+	if (!rb)
+		return;
+
 	if (!rpcrdma_regbuf_is_mapped(rb))
 		return;
 
@@ -1517,9 +1520,6 @@ rpcrdma_dma_unmap_regbuf(struct rpcrdma_regbuf *rb)
 void
 rpcrdma_free_regbuf(struct rpcrdma_regbuf *rb)
 {
-	if (!rb)
-		return;