linux-kernel - Re: strange put

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Date:	Mon, 28 Mar 2011 01:15:36 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Trond Myklebust <Trond.Myklebust@...app.com>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: strange put_rpccred() handling

Trond Myklebust <Trond.Myklebust@...app.com> writes:

> 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?

Yes, of course.

Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>

-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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