linux-kernel - Re: XFS Bug null pointer dereference in xfs_free_ag

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Date:	Tue, 01 Aug 2006 10:12:14 +0200
From:	Jan Dittmer <jdi@....org>
To:	Joe Jin <lkmaillist@...il.com>
CC:	kernel <linux@...center.cn>, Nathan Scott <nathans@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: XFS Bug null pointer dereference in xfs_free_ag_extent

Joe Jin schrieb:
>  From the information, I think it caused by (args.agbp == NULL).
> get rid of, we'll find the call trace should panic:
> xfs_free_extent
> |_   xfs_free_ag_extent  => here args.agbp= NULL;
>         |_ xfs_btree_init_cursor()
>               |_ agf = XFS_BUF_TO_AGF(agbp);  => (xfs_agf_t 
> *)XFS_BUF_PTR(arbp)
>                              |_ (xfs_caddr_t)((agbp)->b_addr) : but 
> here, agbp is NULL
> so it caused the oops.
> Non debug option, and the oops occured at xfs_btree_init_cursor().
> 

Probably caused by this part of the diff from Nathan's earlier mail:

--- 8558226281c45a61d7a0bc056505246e705a372b
+++ 22af489d3f346c7bb4488cdcf1ee91e59e48ddf3
--- fs/xfs/xfs_alloc.c
+++ fs/xfs/xfs_alloc.c

@@ -1951,8 +1951,14 @@ xfs_alloc_fix_freelist(
  		 * the restrictions correctly.  Can happen for free calls
  		 * on a completely full ag.
  		 */
-		if (targs.agbno == NULLAGBLOCK)
+		if (targs.agbno == NULLAGBLOCK) {
+			if (!(flags & XFS_ALLOC_FLAG_FREEING)) {
+				xfs_trans_brelse(tp, agflbp);
+				args->agbp = NULL;
+				return 0;
+			}
  			break;
+		}
  		/*
  		 * Put each allocated block on the list.
  		 */

Jan
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