[issue1276] panic: assertion: volume->io.lock.refs == 0 in hammer_unload_volume

[Matthew Dillon]

:Thomas Nikolajsen <thomas.nikolajsen at mail.dk> added the comment:
:
:New crash dump using HEAD of Feb 12, 2009.
:
:Uploading to leaf as *.29 (with all modules in use).
:
: -thomas

    Thomas, I believe I have found it.  Please try the enclosed patch.
    When a buffer collision occurs under heavy loads a ref on the volume
    structure was not being undone, leading to a ref count leak on the
    volume structure which will result in a panic on umount.

    This fix will not make it into 2.2.  It needs to be tested and verified
    to have fixed the problem, then I'll commit and MFC it.
 	
					-Matt
					Matthew Dillon 
					<dillon at backplane.com>

diff --git a/sys/vfs/hammer/hammer_ondisk.c b/sys/vfs/hammer/hammer_ondisk.c
index 711fe65..214e1ff 100644
--- a/sys/vfs/hammer/hammer_ondisk.c
+++ b/sys/vfs/hammer/hammer_ondisk.c
@@ -639,8 +639,10 @@ again:
 	 * Insert the buffer into the RB tree and handle late collisions.
 	 */
 	if (RB_INSERT(hammer_buf_rb_tree, &hmp->rb_bufs_root, buffer)) {
-		hammer_unref(&buffer->io.lock);
+		hammer_unref(&buffer->io.lock);	/* safety */
 		--hammer_count_buffers;
+		hammer_rel_volume(volume, 0);
+		buffer->io.volume = NULL;	/* safety */
 		kfree(buffer, hmp->m_misc);
 		goto again;
 	}