libceph: avoid unregistering osd request when not registered

There is a race between two __unregister_request() callers: the
reply path and the ceph_osdc_wait_request().  If we get a reply
*and* the timeout expires at roughly the same time, both callers
will try to unregister the request, and the second one will do bad
things.

Simply check if the request is still already unregistered; if so,
return immediately and do nothing.

Fixes http://tracker.newdream.net/issues/2420

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
index b7d633cc96a6..b098e7b591f0 100644
--- a/net/ceph/osd_client.c
+++ b/net/ceph/osd_client.c
@@ -841,6 +841,12 @@ static void register_request(struct ceph_osd_client *osdc,
 static void __unregister_request(struct ceph_osd_client *osdc,
                                  struct ceph_osd_request *req)
 {
+        if (RB_EMPTY_NODE(&req->r_node)) {
+                dout("__unregister_request %p tid %lld not registered\n",
+                        req, req->r_tid);
+                return;
+        }
+
         dout("__unregister_request %p tid %lld\n", req, req->r_tid);
         rb_erase(&req->r_node, &osdc->requests);
         osdc->num_requests--;