[libvirt] [PATCH] nwfilter: Fix the test for the result of atomic dec and test

[Stefan Berger]

From: Stefan Berger <stefanb at linux.vnet.ibm.com>

https://bugzilla.redhat.com/show_bug.cgi?id=1071181

Commit 49b59a15 fixed one problem but masks another one related to pointer
freeing.

Use virAtomicIntGet() to test for 0 rather than trying to test for 'true'
after  virAtomicIntDecAndTest().

Avoid putting of the virNWFilterSnoopReq once the thread has been started.

Signed-off-by: Stefan Berger <stefanb at linux.vnet.ibm.com>
---
 src/nwfilter/nwfilter_dhcpsnoop.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/nwfilter/nwfilter_dhcpsnoop.c b/src/nwfilter/nwfilter_dhcpsnoop.c
index d2a8062..32ca304 100644
--- a/src/nwfilter/nwfilter_dhcpsnoop.c
+++ b/src/nwfilter/nwfilter_dhcpsnoop.c
@@ -720,7 +720,10 @@ virNWFilterSnoopReqPut(virNWFilterSnoopReqPtr req)
 
     virNWFilterSnoopLock();
 
-    if (virAtomicIntDecAndTest(&req->refctr)) {
+    virAtomicIntDecAndTest(&req->refctr);
+
+    /* make sure it's 0; virAtomitIntDecAndTest may return true on '1' */
+    if (virAtomicIntGet(&req->refctr) == 0) {
         /*
          * delete the request:
          * - if we don't find req on the global list anymore
@@ -1605,6 +1608,7 @@ virNWFilterDHCPSnoopReq(virNWFilterTechDriverPtr techdriver,
     int tmp;
     virThread thread;
     virNWFilterVarValuePtr dhcpsrvrs;
+    bool threadPuts = false;
 
     virNWFilterSnoopIFKeyFMT(ifkey, vmuuid, macaddr);
 
@@ -1690,6 +1694,8 @@ virNWFilterDHCPSnoopReq(virNWFilterTechDriverPtr techdriver,
     /* prevent thread from holding req */
     virNWFilterSnoopReqLock(req);
 
+    threadPuts = true;
+
     if (virThreadCreate(&thread, false, virNWFilterDHCPSnoopThread,
                         req) != 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
@@ -1737,7 +1743,8 @@ exit_rem_ifnametokey:
 exit_snoopunlock:
     virNWFilterSnoopUnlock();
 exit_snoopreqput:
-    virNWFilterSnoopReqPut(req);
+    if (!threadPuts)
+        virNWFilterSnoopReqPut(req);
 
     return -1;
 }
-- 
1.8.1.4