linux-kernel - Re: [PATCH 04/13] module: use RCU to synchronize find

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Message-ID: <20210129051012.GA2053@lst.de>
Date:   Fri, 29 Jan 2021 06:10:12 +0100
From:   Christoph Hellwig <hch@....de>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     Christoph Hellwig <hch@....de>,
        Frederic Barrat <fbarrat@...ux.ibm.com>,
        Andrew Donnellan <ajd@...ux.ibm.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Jessica Yu <jeyu@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        live-patching@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 04/13] module: use RCU to synchronize find_module

On Thu, Jan 28, 2021 at 05:50:56PM -0300, Thiago Jung Bauermann wrote:
> >  struct module *find_module(const char *name)
> >  {
> > -	module_assert_mutex();
> 
> Does it make sense to replace the assert above with the warn below (untested)?
> 
>      RCU_LOCKDEP_WARN(rcu_read_lock_sched_held());

One caller actually holds module_mutex still.  And find_module_all,
which implements the actual logic already asserts that either
module_mutex is held or rcu_read_lock, so I don't tink we need an
extra one here.