linux-kernel - Re: [PATCH v2] fs: make generic_fillattr() tail-callable and utilize it in ext2/ext4

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <Z_OSxRO4b7OduCTx@infradead.org>
Date: Mon, 7 Apr 2025 01:54:29 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: Christoph Hellwig <hch@...radead.org>, brauner@...nel.org,
	viro@...iv.linux.org.uk, jack@...e.cz, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] fs: make generic_fillattr() tail-callable and utilize
 it in ext2/ext4

On Fri, Apr 04, 2025 at 10:14:32PM +0200, Mateusz Guzik wrote:
> Callers don't need to check it because it is guaranteed to be 0. Also
> returning 0 vs returning nothing makes virtually no difference to
> anyone.

Nom the return value very clearly states it can return something else
with your patch, and people will sooner or later do that.

Let's stop these silly things that just create nasty landmines for no
reason at all.

> As for general context, there are several small slowdowns when issuing
> fstat() and I'm tackling them bit by bit (and yes, tail calling vs
> returning to the caller and that caller exiting is a small
> optimization).

Please prove that it makes a difference.  And if it does do the
changes in a sane way by keeping the helper as is except for marking
it as inline candidate and a special _tail helper below that inlines
it.

But the bar for such micro-optimizations should be high, and so far you
have no managed to provide any rationale for it.