volser: ensure GCTrans transaction walk remains valid

[openafs.git] / src / volser / voltrans.c

diff --git a/src/volser/voltrans.c b/src/volser/voltrans.c
index d341a2b..7a7af3e 100644 (file)
--- a/src/volser/voltrans.c
+++ b/src/volser/voltrans.c
@@ -20,11 +20,15 @@
 #include <roken.h>
 
 #include <afs/opr.h>
+#ifdef AFS_PTHREAD_ENV
+# include <opr/lock.h>
+#endif
 
 #ifdef AFS_NT40_ENV
 #include <afs/afsutil.h>
 #endif
 
+#include <rx/rx_queue.h>
 #include <afs/afsint.h>
 #include <afs/prs_fs.h>
 #include <afs/nfs.h>
@@ -50,7 +54,7 @@ static afs_int32 transCounter = 1;
 
 /* create a new transaction, returning ptr to same with high ref count */
 struct volser_trans *
-NewTrans(afs_uint32 avol, afs_int32 apart)
+NewTrans(VolumeId avol, afs_int32 apart)
 {
     /* set volid, next, partition */
     struct volser_trans *tt, *newtt;
@@ -176,17 +180,14 @@ GCTrans(void)
 
     VTRANS_LOCK;
     for (tt = allTrans; tt; tt = nt) {
-       nt = tt->next;          /* remember in case we zap it */
        if (tt->time + OLDTRANSWARN < now) {
-           Log("trans %u on volume %u %s than %d seconds\n", tt->tid,
-               tt->volid,
+           Log("trans %u on volume %" AFS_VOLID_FMT " %s than %d seconds\n", tt->tid,
+               afs_printable_VolumeId_lu(tt->volid),
                ((tt->refCount > 0) ? "is older" : "has been idle for more"),
                (((now - tt->time) / GCWAKEUP) * GCWAKEUP));
        }
-       if (tt->refCount > 0)
-           continue;
-       if (tt->time + OLDTRANSTIME < now) {
-           Log("trans %u on volume %u has timed out\n", tt->tid, tt->volid);
+       if ((tt->refCount <= 0) && (tt->time + OLDTRANSTIME < now)) {
+           Log("trans %u on volume %" AFS_VOLID_FMT " has timed out\n", tt->tid, afs_printable_VolumeId_lu(tt->volid));
 
            tt->refCount++;     /* we're using it now */
 
@@ -204,12 +205,27 @@ GCTrans(void)
 
                VTRANS_UNLOCK;
                VPurgeVolume(&error, tt->volume);
+               /*
+                * While the lock was dropped, tt->next may have changed.
+                * Therefore, defer reading tt->next until _after_ we regain the lock.
+                */
                VTRANS_LOCK;
            }
-
-           DeleteTrans(tt, 0); /* drops refCount or deletes it */
+           nt = tt->next;
+           /*
+            * DeleteTrans() will decrement tt->refCount; if it falls to 0, it will
+            * also delete tt itself.  Therefore, we must read tt->next _before_
+            * calling DeleteTrans().
+            */
+           DeleteTrans(tt, 0);
            GCDeletes++;
+           continue;
        }
+       /*
+        * This path never dropped VTRANS_LOCK or modified the allTrans list.
+        * Therefore, no special care is required to determine the next trans in the chain.
+        */
+       nt = tt->next;
     }
     VTRANS_UNLOCK;
     return 0;