macos disconnected vnode holding fix

tweak how we hold vcaches to avoid issues with the underlying
vnode having an iocount underrun due to races.

Change-Id: I96526ed52c11aac1124a8cf66458ba3e25e7efb2
Reviewed-on: http://gerrit.openafs.org/2501
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>

src/afs/DARWIN/osi_vnodeops.c

@@ -2206,6 +2206,26 @@ afs_darwin_finalizevnode(struct vcache *avc, struct vnode *dvp, struct component
 	}
 	avc->v = nvp;
 	avc->f.states &=~ CDeadVnode;
+	/* If we were carrying an extra ref for dirty, hold/push it. */
+	if (avc->f.ddirty_flags) {
+	    vnode_get(nvp);
+	    vnode_ref(nvp);
+	}
+	/* If we were carrying an extra ref for shadow, hold/push it. */
+	if (avc->f.shadow.vnode) {
+	    vnode_get(nvp);
+	    vnode_ref(nvp);
+	}
+    }
+    /* Drop any extra dirty ref on the old vnode */
+    if (avc->f.ddirty_flags) {
+	vnode_put(ovp);
+	vnode_rele(ovp);
+    }
+    /* Drop any extra shadow ref on the old vnode */
+    if (avc->f.shadow.vnode) {
+	vnode_put(ovp);
+	vnode_rele(ovp);
     }
     vnode_put(ovp);
     vnode_rele(ovp);

src/afs/afs_dcache.c

@@ -3399,7 +3399,7 @@ afs_MakeShadowDir(struct vcache *avc, struct dcache *adc)
 	ObtainWriteLock(&afs_xvcache, 763);
 	ObtainWriteLock(&afs_disconDirtyLock, 765);
 	QAdd(&afs_disconShadow, &avc->shadowq);
-	osi_vnhold(avc, 0);
+	osi_Assert((afs_RefVCache(avc) == 0));
 	ReleaseWriteLock(&afs_disconDirtyLock);
 	ReleaseWriteLock(&afs_xvcache);
 

src/afs/afs_prototypes.h

@@ -1044,6 +1044,7 @@ extern struct vcache *afs_GetVCache(register struct VenusFid *afid,
 				    struct vrequest *areq, afs_int32 * cached,
 				    struct vcache *avc);
 extern void afs_PutVCache(register struct vcache *avc);
+extern int afs_RefVCache(struct vcache *avc);
 extern void afs_ProcessFS(register struct vcache *avc,
 			  register struct AFSFetchStatus *astat,
 			  struct vrequest *areq);

src/afs/afs_vcache.c

@@ -2531,6 +2531,45 @@ findvc_sleep(struct vcache *avc, int flag)
 	}
     }
 }
+
+/*!
+ * Add a reference on an existing vcache entry.
+ *
+ * \param tvc Pointer to the vcache.
+ *
+ * \note Environment: Must be called with at least one reference from
+ * elsewhere on the vcache, even if that reference will be dropped.
+ * The global lock is required.
+ *
+ * \return 0 on success, -1 on failure.
+ */
+
+int
+afs_RefVCache(struct vcache *tvc)
+{
+#ifdef AFS_DARWIN80_ENV
+    vnode_t tvp;
+#endif
+
+    /* AFS_STATCNT(afs_RefVCache); */
+
+#ifdef  AFS_DARWIN80_ENV
+    tvp = AFSTOV(tvc);
+    if (vnode_get(tvp))
+	return -1;
+    if (vnode_ref(tvp)) {
+	AFS_GUNLOCK();
+	/* AFSTOV(tvc) may be NULL */
+	vnode_put(tvp);
+	AFS_GLOCK();
+	return -1;
+    }
+#else
+	osi_vnhold(tvc, 0);
+#endif
+    return 0;
+}				/*afs_RefVCache */
+
 /*!
  * Find a vcache entry given a fid.
  *

src/afs/discon.h

@@ -56,7 +56,7 @@ static_inline void afs_DisconAddDirty(struct vcache *avc, int operation, int loc
 	    ObtainWriteLock(&afs_xvcache, 702);
 	ObtainWriteLock(&afs_disconDirtyLock, 703);
 	QAdd(&afs_disconDirty, &avc->dirtyq);
-	osi_vnhold(avc, 0);
+	osi_Assert((afs_RefVCache(avc) == 0));
 	ReleaseWriteLock(&afs_disconDirtyLock);
 	if (lock)
 	    ReleaseWriteLock(&afs_xvcache);