DAFS: Do not let VScheduleSalvage_r free vp

In VScheduleSalvage_r, we were calling VCancelReservation_r, which has
the possibility of free'ing vp. Since we still use vp after doing this
(and since we're already inside VCancelReservation_r to begin with),
we must not free vp. Instead, just decrement nWaiters without
triggering any of the dtor code in VCancelReservation_r. This is safe
as long as all VScheduleSalvage_r callers ensure that they check to
free the vp if necessary, which they all do.

Thanks to Derrick Brashear.

Reviewed-on: http://gerrit.openafs.org/3272
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit ef4b9e13ef6a79d7e5f540297e486189fdedf085)
Change-Id: I2f49d5eb6f9bad2343ee9a9c84ccbc1f323cc8a8
Reviewed-on: http://gerrit.openafs.org/3479

diff --git a/src/vol/volume.c b/src/vol/volume.c
index 8ebc10284044b451341be9797295442b01b55eb2..0c90121cfe0ccb2a7806865e46100914a8b8f334 100644 (file)
--- a/src/vol/volume.c
+++ b/src/vol/volume.c
@@ -4952,6 +4952,10 @@ VOfflineForSalvage_r(struct Volume *vp)
  *
  * @note this is one of the event handlers called by VCancelReservation_r
  *
+ * @note the caller must check if the volume needs to be freed after calling
+ *       this; the volume may not have any references or be on any lists after
+ *       we return, and we do not free it
+ *
  * @see VCancelReservation_r
  *
  * @internal volume package internal use only.
@@ -5226,6 +5230,10 @@ try_FSSYNC(Volume *vp, char *partName, int *code) {
  * server over SALVSYNC. If we are not the fileserver, the request will be
  * sent to the fileserver over FSSYNC (FSYNC_VOL_FORCE_ERROR/FSYNC_SALVAGE).
  *
+ * @note the caller must check if the volume needs to be freed after calling
+ *       this; the volume may not have any references or be on any lists after
+ *       we return, and we do not free it
+ *
  * @note DAFS only
  *
  * @internal volume package internal use only.
@@ -5318,7 +5326,14 @@ VScheduleSalvage_r(Volume * vp)
            }
        }
     }
-    VCancelReservation_r(vp);
+
+    /* NB: this is cancelling the reservation we obtained above, but we do
+     * not call VCancelReservation_r, since that may trigger the vp dtor,
+     * possibly free'ing the vp. We need to keep the vp around after
+     * this, as the caller may reference vp without any refs. Instead, it
+     * is the duty of the caller to inspect 'vp' after we return to see if
+     * needs to be freed. */
+    osi_Assert(--vp->nWaiters >= 0);
     return ret;
 }
 #endif /* SALVSYNC_BUILD_CLIENT || FSSYNC_BUILD_CLIENT */