Date: Mon, 29 May 2006 18:36:24 -0700
From: Andrew Morton <akpm@osdl.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org, arjan@infradead.org
Subject: Re: [patch 55/61] lock validator: special locking: sb->s_umount
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References: <20060529212109.GA2058@elte.hu>
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On Mon, 29 May 2006 23:27:32 +0200
Ingo Molnar <mingo@elte.hu> wrote:

> From: Ingo Molnar <mingo@elte.hu>
> 
> workaround for special sb->s_umount locking rule.
> 
> s_umount gets held across a series of lock dropping and releasing
> in prune_one_dentry(), so i changed the order, at the risk of
> introducing a umount race. FIXME.
> 
> i think a better fix would be to do the unlocks as _non_nested in
> prune_one_dentry(), and to do the up_read() here as
> an up_read_non_nested() as well?
> 
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
> ---
>  fs/dcache.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> Index: linux/fs/dcache.c
> ===================================================================
> --- linux.orig/fs/dcache.c
> +++ linux/fs/dcache.c
> @@ -470,8 +470,9 @@ static void prune_dcache(int count, stru
>  		s_umount = &dentry->d_sb->s_umount;
>  		if (down_read_trylock(s_umount)) {
>  			if (dentry->d_sb->s_root != NULL) {
> -				prune_one_dentry(dentry);
> +// lockdep hack: do this better!
>  				up_read(s_umount);
> +				prune_one_dentry(dentry);
>  				continue;

argh, you broke my kernel!

I'll whack some ifdefs in here so it's only known-broken if CONFIG_LOCKDEP.

Again, we'd need the real fix here.
-
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