xvcb lock order violation

[openafs.git] / src / afs / afs_server.c

diff --git a/src/afs/afs_server.c b/src/afs/afs_server.c
index 1baa80b..bcff775 100644 (file)
--- a/src/afs/afs_server.c
+++ b/src/afs/afs_server.c
@@ -1580,9 +1580,9 @@ afs_SetServerPrefs(struct srvAddr *sa)
 /* afs_FlushServer()
  * The addresses on this server struct has changed in some way and will
  * clean up all other structures that may reference it.
- * The afs_xserver and afs_xsrvAddr locks are assumed taken.
+ * The afs_xserver, afs_xvcb and afs_xsrvAddr locks are assumed taken.
  */
-void
+static void
 afs_FlushServer(struct server *srvp)
 {
     afs_int32 i;
@@ -1598,12 +1598,10 @@ afs_FlushServer(struct server *srvp)
     if (srvp->cbrs) {
        struct afs_cbr *cb, *cbnext;
 
-         ObtainWriteLock(&afs_xvcb, 300);
        for (cb = srvp->cbrs; cb; cb = cbnext) {
            cbnext = cb->next;
            afs_FreeCBR(cb);
        } srvp->cbrs = (struct afs_cbr *)0;
-       ReleaseWriteLock(&afs_xvcb);
     }
 
     /* If no more srvAddr structs hanging off of this server struct,
@@ -1719,6 +1717,23 @@ afs_GetCapabilities(struct server *ts)
 
 }
 
+static struct server *
+afs_SearchServer(u_short aport, afsUUID * uuidp, afs_int32 locktype,
+                struct server **oldts, afs_int32 addr_uniquifier)
+{
+    struct server *ts = afs_FindServer(0, aport, uuidp, locktype);
+    if (ts && (ts->sr_addr_uniquifier == addr_uniquifier) && ts->addr) {
+       /* Found a server struct that is multihomed and same
+        * uniqufier (same IP addrs). The above if statement is the
+        * same as in InstallUVolumeEntry().
+        */
+       return ts;
+    }
+    if (ts)
+       *oldts = ts;            /* Will reuse if same uuid */
+    return NULL;
+}
+
 /* afs_GetServer()
  * Return an updated and properly initialized server structure
  * corresponding to the server ID, cell, and port specified.
@@ -1756,22 +1771,37 @@ afs_GetServer(afs_uint32 * aserverp, afs_int32 nservers, afs_int32 acell,
     } else {
        if (nservers <= 0)
            panic("afs_GetServer: incorrect count of servers");
-       ts = afs_FindServer(0, aport, uuidp, locktype);
-       if (ts && (ts->sr_addr_uniquifier == addr_uniquifier) && ts->addr) {
-           /* Found a server struct that is multihomed and same
-            * uniqufier (same IP addrs). The above if statement is the
-            * same as in InstallUVolumeEntry().
-            */
+
+       ts = afs_SearchServer(aport, uuidp, locktype, &oldts, addr_uniquifier);
+       if (ts) {
            ReleaseSharedLock(&afs_xserver);
            return ts;
        }
-       if (ts)
-           oldts = ts;         /* Will reuse if same uuid */
     }
 
-    UpgradeSToWLock(&afs_xserver, 36);
+    /*
+     * Lock hierarchy requires xvcb, then xserver. We *have* xserver.
+     * Do a little dance and see if we can grab xvcb. If not, we
+     * need to recheck that oldts is still right after a drop and reobtain.
+     */
+    if (EWOULDBLOCK == NBObtainWriteLock(&afs_xvcb, 300)) {
+       ReleaseSharedLock(&afs_xserver);
+       ObtainWriteLock(&afs_xvcb, 299);
+       ObtainWriteLock(&afs_xserver, 35);
+
+       /* we don't know what changed while we didn't hold the lock */
+       oldts = 0;
+       ts = afs_SearchServer(aport, uuidp, locktype, &oldts,
+                             addr_uniquifier);
+       if (ts) {
+           ReleaseWriteLock(&afs_xserver);
+           ReleaseWriteLock(&afs_xvcb);
+           return ts;
+       }
+    } else {
+       UpgradeSToWLock(&afs_xserver, 36);
+    }
     ObtainWriteLock(&afs_xsrvAddr, 116);
-
     srvcount = afs_totalServers;
 
     /* Reuse/allocate a new server structure */
@@ -1901,6 +1931,8 @@ afs_GetServer(afs_uint32 * aserverp, afs_int32 nservers, afs_int32 acell,
            orphsa->sa_flags &= ~SRVADDR_MH;    /* Not multihomed */
        }
     }
+    /* We can't need this below, and won't reacquire */
+    ReleaseWriteLock(&afs_xvcb);
 
     srvcount = afs_totalServers - srvcount;    /* # servers added and removed */
     if (srvcount) {