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Subject: Re: strange put_rpccred() handling
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: "J. Bruce Fields" <bfields@fieldses.org>, linux-kernel@vger.kernel.org,
        linux-nfs@vger.kernel.org
In-Reply-To: <87ei5sppsx.fsf@devron.myhome.or.jp>
References: <87ei5sppsx.fsf@devron.myhome.or.jp>
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Date: Sun, 27 Mar 2011 17:55:03 +0200
Message-ID: <1301241303.22136.31.camel@lade.trondhjem.org>
Sender: linux-nfs-owner@vger.kernel.org
List-ID: <linux-nfs.vger.kernel.org>
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On Mon, 2011-03-28 at 00:05 +0900, OGAWA Hirofumi wrote:
> Hi,
> 
> BUG: atomic_dec_and_test(): -1: atomic counter underflow at:
> Pid: 2827, comm: mount.nfs Not tainted 2.6.38 #1
> Call Trace:
>  [<ffffffffa02223a0>] ? put_rpccred+0x44/0x14e [sunrpc]
>  [<ffffffffa021bbe9>] ? rpc_ping+0x4e/0x58 [sunrpc]
>  [<ffffffffa021c4a5>] ? rpc_create+0x481/0x4fc [sunrpc]
>  [<ffffffffa022298a>] ? rpcauth_lookup_credcache+0xab/0x22d [sunrpc]
>  [<ffffffffa028be8c>] ? nfs_create_rpc_client+0xa6/0xeb [nfs]
>  [<ffffffffa028c660>] ? nfs4_set_client+0xc2/0x1f9 [nfs]
>  [<ffffffffa028cd3c>] ? nfs4_create_server+0xf2/0x2a6 [nfs]
>  [<ffffffffa0295d07>] ? nfs4_remote_mount+0x4e/0x14a [nfs]
>  [<ffffffff810dd570>] ? vfs_kern_mount+0x6e/0x133
>  [<ffffffffa029605a>] ? nfs_do_root_mount+0x76/0x95 [nfs]
>  [<ffffffffa029643d>] ? nfs4_try_mount+0x56/0xaf [nfs]
>  [<ffffffffa0297434>] ? nfs_get_sb+0x435/0x73c [nfs]
>  [<ffffffff810dd59b>] ? vfs_kern_mount+0x99/0x133
>  [<ffffffff810dd693>] ? do_kern_mount+0x48/0xd8
>  [<ffffffff810f5b75>] ? do_mount+0x6da/0x741
>  [<ffffffff810f5c5f>] ? sys_mount+0x83/0xc0
>  [<ffffffff8100293b>] ? system_call_fastpath+0x16/0x1b
> 
> This is not oops, and debug code is not in vanilla. This debug code is
> simple - detects atomic_dec_and_test() underflow.
> 
> Well, so, I think this is real bug of nfs codes somewhere. With some
> review, the code
> 
> rpc_call_sync()
>     rpc_run_task
>         rpc_execute()
>             __rpc_execute()
>                 rpc_release_task()
>                     rpc_release_resources_task()
>                         put_rpccred()                <= release cred
>     rpc_put_task
>         rpc_do_put_task()
>             rpc_release_resources_task()
>                 put_rpccred()                        <= release cred again
> 
> seems to be release cred unintendedly.
> 
> static void rpc_release_resources_task(struct rpc_task *task)
> {
> 	if (task->tk_rqstp)
> 		xprt_release(task);
> 	if (task->tk_msg.rpc_cred) {
> 		put_rpccred(task->tk_msg.rpc_cred);
> 		task->tk_msg.rpc_cred = NULL;
> 	}
> 	rpc_task_release_client(task);
> }

May I add a signed-off-by from you, and just push the above fix to
Linus?

Cheers
  Trond

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com