From 0eb68f307aac84472a13523a0ce8b7a865f01ac7 Mon Sep 17 00:00:00 2001
From: Derrick Brashear <shadow@dementia.org>
Date: Tue, 14 May 2002 21:21:09 +0000
Subject: [PATCH] 
 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
---
 src/dir/buffer.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/dir/buffer.c b/src/dir/buffer.c
index 376ba81f5d..018ddca06f 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;
 }