linux-kernel - Re: [PATCH 16/24] link_path

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Message-ID: <CA+55aFw7_3DFbbY0==XOL_FFv28vpD-KphK+7nr7xaVVE7Twgg@mail.gmail.com>
Date:	Mon, 20 Apr 2015 14:41:31 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Neil Brown <neilb@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 16/24] link_path_walk: kill the recursion

On Mon, Apr 20, 2015 at 2:32 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> A kilobyte would suffice for 32 levels.  _IF_ we go for "lift the restrictions
> on nesting completely", sure, we want to switch to (on-demand) dynamic
> allocation.

And no, we will *never* lift the recursion limit. Not for 1kB, not for
1MB. Never.

Because it's a latency and DoS issue too. We need to react well to
true loops, but also to "very deep" non-loops. It's not about memory
use, it's about users triggering unreasonable CPU resources.

                      Linus
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