Don't hold on to the afs_xvcache lock while creating a symlink

Holding the afs_xvcache lock over the RPC while creating a symlink is a
severe blow to performance as look-ups from other tasks likely
require the lock. Drop the lock and rely solely on the fileserver
to detect a clash with a same entry created simultaneously.

Change-Id: Ia6de353bd9dc003addf5f3be7a8f3e769247a513
Reviewed-on: http://gerrit.openafs.org/2233
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>

diff --git a/src/afs/VNOPS/afs_vnop_symlink.c b/src/afs/VNOPS/afs_vnop_symlink.c
index 691b3b5..c09c35f 100644 (file)
--- a/src/afs/VNOPS/afs_vnop_symlink.c
+++ b/src/afs/VNOPS/afs_vnop_symlink.c
@@ -153,8 +153,9 @@ afs_symlink(OSI_VC_DECL(adp), char *aname, struct vattr *attrs,
     ObtainWriteLock(&adp->lock, 156);
     if (tdc)
        ObtainWriteLock(&tdc->lock, 636);
-    ObtainSharedLock(&afs_xvcache, 17);        /* prevent others from creating this entry */
-    /* XXX Pay attention to afs_xvcache around the whole thing!! XXX */
+    /* No further locks: if the SymLink succeeds, it does not matter what happens
+     * to our local copy of the directory. If somebody tampers with it in the meantime,
+     * the copy will be invalidated */
     if (!AFS_IS_DISCON_RW) {
        do {
            tc = afs_Conn(&adp->f.fid, &treq, SHARED_LOCK);
@@ -195,7 +196,7 @@ afs_symlink(OSI_VC_DECL(adp), char *aname, struct vattr *attrs,
 #endif
     }
 
-    UpgradeSToWLock(&afs_xvcache, 40);
+    ObtainWriteLock(&afs_xvcache, 40);
     if (code) {
        if (code < 0) {
            ObtainWriteLock(&afs_xcbhash, 499);
@@ -216,6 +217,8 @@ afs_symlink(OSI_VC_DECL(adp), char *aname, struct vattr *attrs,
     if (AFS_IS_DISCON_RW || afs_LocalHero(adp, tdc, &OutDirStatus, 1)) {
        /* we can do it locally */
        ObtainWriteLock(&afs_xdcache, 293);
+       /* If the following fails because the name has been created in the meantime, the
+        * directory is out-of-date - the file server knows best! */
        code = afs_dir_Create(tdc, aname, &newFid.Fid);
        ReleaseWriteLock(&afs_xdcache);
        if (code && !AFS_IS_DISCON_RW) {