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Date:	Thu, 12 Sep 2013 17:56:08 -0700
From:	Linus Torvalds <>
To:	Al Viro <>
Cc:	Andrew Morton <>,
	Stephen Rothwell <>,
	linux-next <>,
	Linux Kernel Mailing List <>,
	Dave Chinner <>,
	Glauber Costa <>
Subject: Re: linux-next: manual merge of the akpm tree with Linus' tree

On Tue, Sep 10, 2013 at 4:37 PM, Linus Torvalds
<> wrote:
> From a quick look, this looks pretty broken:
>     if (list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru))
>         this_cpu_inc(nr_dentry_unused);
>     dentry->d_flags |= DCACHE_LRU_LIST;
> because if that list_lru_add() can fail, then we shouldn't set the
> DCACHE_LRU_LIST bit either.
> That said, I don't see how it can fail. We only do this with the
> dentry locked, and when it's not already on the LRU list. So I think
> the "if()" is just misleading and unnecessary - but the code works.

So I thought you'd clean this up. Looking again, it still seems really
confused, and I'm finding actual bugs.

You don't clear the DCACHE_LRU_LIST when you remove dentries from the
d_lru list. In other cases (like shrink_dentry_list), you clear just

As a result, the "if ()" isn't necessarily unnecessary, but there are
actual bugs. It looks like the dentry can be removed from the d_lru
lists without the bit ever getting cleared, and if that happens, it
will never be moved back.

The rule for DCACHE_LRU_LIST was - and should be - that the bit is set
IFF the d_lru list is not empty. So it gets set when a dentry is moved
to the LRU lists, but it _stays_ set if the dentry is moved to the
shrink_list. It then gets cleared when the dentry is removed from any
d_lru list (ie "list_del_init()").

I'll walk through the code, it looked suspicious. Maybe there's
something subtle that makes it work, but I don't see it.

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