From: Derrick Brashear <shadow@dementia.org>
Date: Tue, 14 May 2002 21:21:09 +0000 (+0000)
Subject: dir-hold-afs-bufferlock-across-increment-of-buffer-lockers-to-prevent-newslot-from... 
X-Git-Tag: openafs-devel_1_3_3~130
X-Git-Url: https://git.michaelhowe.org/gitweb/?a=commitdiff_plain;h=0eb68f307aac84472a13523a0ce8b7a865f01ac7;p=packages%2Fo%2Fopenafs.git

dir-hold-afs-bufferlock-across-increment-of-buffer-lockers-to-prevent-newslot-from-walking-on-stuff-20020514


liberal debugging code and hammering produced a failure where newslot was
actually walking on another call to newslot because the bufferlock was
being dropped before newslot incremented lockers on the buffer it
was allocating, allowing someone else to come along and also think they
could allocate it.

by holding the bufferlock just a little longer we avoid this
---

diff --git a/src/dir/buffer.c b/src/dir/buffer.c
index 376ba81f5..018ddca06 100644
--- a/src/dir/buffer.c
+++ b/src/dir/buffer.c
@@ -132,8 +132,8 @@ char *DRead(fid,page)
     if ( tb = phTable[pHash(fid)] ) {  /* ASSMT HERE */
 	if (bufmatch(tb)) {
 	    ObtainWriteLock(&tb->lock);
-	    ReleaseWriteLock(&afs_bufferLock);
 	    tb->lockers++;
+	    ReleaseWriteLock(&afs_bufferLock);
 	    tb->accesstime = ++timecounter;
 	    ReleaseWriteLock(&tb->lock);
 	    return tb->data;
@@ -144,8 +144,8 @@ char *DRead(fid,page)
 	    if (bufmatch(tb2)) {
 	      buf_Front(bufhead,tb,tb2);
 	      ObtainWriteLock(&tb2->lock);
-	      ReleaseWriteLock(&afs_bufferLock);
 	      tb2->lockers++;
+	      ReleaseWriteLock(&afs_bufferLock);
 	      tb2->accesstime = ++timecounter;
 	      ReleaseWriteLock(&tb2->lock);
 	      return tb2->data;
@@ -154,8 +154,8 @@ char *DRead(fid,page)
 	      if (bufmatch(tb)) {
 		buf_Front(bufhead,tb2,tb);
 		ObtainWriteLock(&tb->lock);
-		ReleaseWriteLock(&afs_bufferLock);
 		tb->lockers++;
+		ReleaseWriteLock(&afs_bufferLock);
 		tb->accesstime = ++timecounter;
 		ReleaseWriteLock(&tb->lock);
 		return tb->data;
@@ -175,8 +175,8 @@ char *DRead(fid,page)
     tb = newslot(fid, page, (tb ? tb : tb2));
     ios++;
     ObtainWriteLock(&tb->lock);
-    ReleaseWriteLock(&afs_bufferLock);
     tb->lockers++;
+    ReleaseWriteLock(&afs_bufferLock);
     if (ReallyRead(tb->fid,tb->page,tb->data)) {
 	tb->lockers--;
         FidZap(tb->fid);	/* disaster */
@@ -399,8 +399,8 @@ char *DNew (fid,page)
 	return 0;
     }
     ObtainWriteLock(&tb->lock);
-    ReleaseWriteLock(&afs_bufferLock);
     tb->lockers++;
+    ReleaseWriteLock(&afs_bufferLock);
     ReleaseWriteLock(&tb->lock);
     return tb->data;
 }