From mboxrd@z Thu Jan  1 00:00:00 1970
From: Matthew Wilcox <matthew@wil.cx>
Subject: Re: [PATCH 2/5 -tip] cifs: umount_begin BKL pushdown
Date: Thu, 23 Apr 2009 13:19:35 -0600
Message-ID: <20090423191934.GW1926@parisc-linux.org>
References: <1240513925-5603-1-git-send-email-abogani@texware.it> <1240513925-5603-2-git-send-email-abogani@texware.it> <1240513925-5603-3-git-send-email-abogani@texware.it>
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Cc: Ingo Molnar <mingo@elte.hu>, Jonathan Corbet <corbet@lwn.net>,
	Fr??d??ric Weisbecker <fweisbec@gmail.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	LKML <linux-kernel@vger.kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	LFSDEV <linux-fsdevel@vger.kernel.org>
To: Alessio Igor Bogani <abogani@texware.it>
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On Thu, Apr 23, 2009 at 09:12:02PM +0200, Alessio Igor Bogani wrote:
> @@ -525,18 +526,26 @@ static void cifs_umount_begin(struct super_block *sb)
>  	struct cifs_sb_info *cifs_sb = CIFS_SB(sb);
>  	struct cifsTconInfo *tcon;
>  
> -	if (cifs_sb == NULL)
> +	lock_kernel();
> +
> +	if (cifs_sb == NULL) {
> +		unlock_kernel();
>  		return;

OK, what are you doing here?  Either the BKL protects the sb here,
and you need to lock_kernel() before calling CIFS_SB(sb), or the BKL
protects nothing, and the lock_kernel() should be moved down below the
test for cifs_sb.

> +	}
>  
>  	tcon = cifs_sb->tcon;
> -	if (tcon == NULL)
> +	if (tcon == NULL) {
> +		unlock_kernel();
>  		return;
> +	}

Likewise -- does cifs rely on the BKL to protect the 'tcon' or not?

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."