linux-kernel - Re: [PATCH] Fix panic in __d_lookup with high dentry hashtable counts

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Message-ID: <20120113162236.GK23916@ZenIV.linux.org.uk>
Date:	Fri, 13 Jan 2012 16:22:36 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dimitri Sivanich <sivanich@....com>
Cc:	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Avi Kivity <avi@...hat.com>,
	linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Fix panic in __d_lookup with high dentry hashtable counts

On Fri, Jan 13, 2012 at 09:52:37AM -0600, Dimitri Sivanich wrote:
> When the number of dentry cache hash table entries gets too high
> (2147483648 entries), use of a signed integer in the initialization
> loop prevents the dentry_hashtable from getting initialized, resulting
> in a panic in __d_lookup.  Fixing this in dcache_init and a few other
> spots for consistency.

>  static void __init dcache_init(void)
>  {
> -	int loop;
> +	long loop;

You've got to be kidding.  Note that D_HASHMASK is at most 32bit.  Use
of long here is an overkill and so's 2^31 hash buckets (that's what,
16Gb in hash list heads alone?  What kind of average chain length do
you expect, BTW?)

Can alloc_large_system_hash() produce the horrors that large, anyway?
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