linux-kernel - Re: [PATCH v2 03/28] vsprintf: %pf(%p)

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Message-ID: <YodF6C9ib2/kh5px@dhcp22.suse.cz>
Date:   Fri, 20 May 2022 09:40:24 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Kent Overstreet <kent.overstreet@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
        pmladek@...e.com, rostedt@...dmis.org, senozhatsky@...omium.org,
        andriy.shevchenko@...ux.intel.com, willy@...radead.org
Subject: Re: [PATCH v2 03/28] vsprintf: %pf(%p)

On Thu 19-05-22 13:23:56, Kent Overstreet wrote:
[...]
> The goal is to replace most of our %p format extensions with this
> interface, and to move pretty-printers out of the core vsprintf.c code -
> this will get us better organization and better discoverability (you'll
> be able to cscope to pretty printer calls!), as well as eliminate a lot
> of dispatch code in vsprintf.c.

Is this really something that we want? While I do see arguments about
our existing %p$FOO mess there is at least one good argument to have all
those "pretty printers" at a single location. That approach allows to do
a proper review whether those printers are safe from the printk point of
view. If we allow any random callback to be called from the printk
context we just give a free ticket to anybody to do whatever from there
without understanding of all potential consequences. 

Maybe that is less of a concern these days when printk locking has been
reworked a lot but I still do remember how frustrating it is to debug
issues related to printk getting stuck...
-- 
Michal Hocko
SUSE Labs