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From: Christoph Hellwig <hch@lst.de>
To: Miroslav Benes <mbenes@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>,
	Frederic Barrat <fbarrat@linux.ibm.com>,
	Andrew Donnellan <ajd@linux.ibm.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Jessica Yu <jeyu@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Jiri Kosina <jikos@kernel.org>, Petr Mladek <pmladek@suse.com>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	dri-devel@lists.freedesktop.org, live-patching@vger.kernel.org,
	linux-kbuild@vger.kernel.org
Subject: Re: [PATCH 04/13] module: use RCU to synchronize find_module
Date: Mon, 1 Feb 2021 12:46:49 +0100	[thread overview]
Message-ID: <20210201114649.GA19696@lst.de> (raw)
In-Reply-To: <alpine.LSU.2.21.2101291626080.22237@pobox.suse.cz>

On Fri, Jan 29, 2021 at 04:29:02PM +0100, Miroslav Benes wrote:
> >  
> > -	mutex_lock(&module_mutex);
> > +	rcu_read_lock_sched();
> >  	/*
> >  	 * We do not want to block removal of patched modules and therefore
> >  	 * we do not take a reference here. The patches are removed by
> > @@ -74,7 +75,7 @@ static void klp_find_object_module(struct klp_object *obj)
> >  	if (mod && mod->klp_alive)
> 
> RCU always baffles me a bit, so I'll ask. Don't we need 
> rcu_dereference_sched() here? "mod" comes from a RCU-protected list, so I 
> wonder.

rcu_dereference* is only used for dereferencing points where that
reference itself is RCU protected, that is the lookup of mod itself down
in find_module_all in this case.

WARNING: multiple messages have this Message-ID
From: Christoph Hellwig <hch@lst.de>
To: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.com>, Jiri Kosina <jikos@kernel.org>,
	Andrew Donnellan <ajd@linux.ibm.com>,
	linux-kbuild@vger.kernel.org, David Airlie <airlied@linux.ie>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	linux-kernel@vger.kernel.org, Maxime Ripard <mripard@kernel.org>,
	live-patching@vger.kernel.org,
	Michal Marek <michal.lkml@markovi.net>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	dri-devel@lists.freedesktop.org,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Jessica Yu <jeyu@kernel.org>,
	Frederic Barrat <fbarrat@linux.ibm.com>,
	Daniel Vetter <daniel@ffwll.ch>,
	linuxppc-dev@lists.ozlabs.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 04/13] module: use RCU to synchronize find_module
Date: Mon, 1 Feb 2021 12:46:49 +0100	[thread overview]
Message-ID: <20210201114649.GA19696@lst.de> (raw)
In-Reply-To: <alpine.LSU.2.21.2101291626080.22237@pobox.suse.cz>

On Fri, Jan 29, 2021 at 04:29:02PM +0100, Miroslav Benes wrote:
> >  
> > -	mutex_lock(&module_mutex);
> > +	rcu_read_lock_sched();
> >  	/*
> >  	 * We do not want to block removal of patched modules and therefore
> >  	 * we do not take a reference here. The patches are removed by
> > @@ -74,7 +75,7 @@ static void klp_find_object_module(struct klp_object *obj)
> >  	if (mod && mod->klp_alive)
> 
> RCU always baffles me a bit, so I'll ask. Don't we need 
> rcu_dereference_sched() here? "mod" comes from a RCU-protected list, so I 
> wonder.

rcu_dereference* is only used for dereferencing points where that
reference itself is RCU protected, that is the lookup of mod itself down
in find_module_all in this case.

  reply	other threads:[~2021-02-01 11:47 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-28 18:14 module loader dead code removal and cleanups v2 Christoph Hellwig
2021-01-28 18:14 ` Christoph Hellwig
2021-01-28 18:14 ` [PATCH 01/13] powerpc/powernv: remove get_cxl_module Christoph Hellwig
2021-01-28 18:14   ` Christoph Hellwig
2021-01-28 18:14 ` [PATCH 02/13] drm: remove drm_fb_helper_modinit Christoph Hellwig
2021-02-03 10:34   ` Daniel Vetter
2021-02-03 10:34     ` Daniel Vetter
2021-02-03 10:34     ` Daniel Vetter
2021-02-03 10:49     ` Christoph Hellwig
2021-01-28 18:14 ` [PATCH 03/13] module: unexport find_module and module_mutex Christoph Hellwig
2021-01-28 18:14   ` Christoph Hellwig
2021-01-29 15:16   ` Miroslav Benes
2021-01-28 18:14 ` [PATCH 04/13] module: use RCU to synchronize find_module Christoph Hellwig
2021-01-28 18:14   ` Christoph Hellwig
2021-01-28 20:50   ` Thiago Jung Bauermann
2021-01-28 20:50     ` Thiago Jung Bauermann
2021-01-28 20:50     ` Thiago Jung Bauermann
2021-01-29  5:10     ` Christoph Hellwig
2021-01-29  5:10       ` Christoph Hellwig
2021-01-29 21:29       ` Thiago Jung Bauermann
2021-01-29 21:29         ` Thiago Jung Bauermann
2021-01-29 10:04   ` Petr Mladek
2021-01-29 10:04     ` Petr Mladek
2021-01-29 15:29   ` Miroslav Benes
2021-02-01 11:46     ` Christoph Hellwig [this message]
2021-02-01 11:46       ` Christoph Hellwig
2021-02-01 12:10     ` Jessica Yu
2021-02-01 12:10       ` Jessica Yu
2021-02-01 12:10       ` Jessica Yu
2021-02-01 13:16       ` Miroslav Benes
2021-02-01 13:16         ` Miroslav Benes
2021-02-01 13:16         ` Miroslav Benes
2021-01-28 18:14 ` [PATCH 05/13] kallsyms: refactor {,module_}kallsyms_on_each_symbol Christoph Hellwig
2021-01-29  9:43   ` Petr Mladek
2021-02-01 11:47     ` Christoph Hellwig
2021-02-01 11:47       ` Christoph Hellwig
2021-02-01 13:37       ` Miroslav Benes
2021-02-01 13:37         ` Miroslav Benes
2021-02-01 13:37         ` Miroslav Benes
2021-02-01 16:28         ` Christoph Hellwig
2021-02-01 16:28           ` Christoph Hellwig
2021-02-02 10:45           ` Miroslav Benes
2021-02-02 10:45             ` Miroslav Benes
2021-02-02 10:45             ` Miroslav Benes
2021-02-01 14:02   ` Miroslav Benes
2021-02-01 14:02     ` Miroslav Benes
2021-02-01 14:02     ` Miroslav Benes
2021-01-28 18:14 ` [PATCH 06/13] kallsyms: only build {, module_}kallsyms_on_each_symbol when required Christoph Hellwig
2021-01-28 18:14 ` [PATCH 07/13] module: mark module_mutex static Christoph Hellwig
2021-01-28 18:14   ` Christoph Hellwig
2021-01-28 18:14 ` [PATCH 08/13] module: remove each_symbol_in_section Christoph Hellwig
2021-01-28 18:14 ` [PATCH 09/13] module: merge each_symbol_section into find_symbol Christoph Hellwig
2021-01-28 18:14 ` [PATCH 10/13] module: pass struct find_symbol_args to find_symbol Christoph Hellwig
2021-01-28 18:14   ` Christoph Hellwig
2021-01-28 18:14 ` [PATCH 11/13] module: move struct symsearch to module.c Christoph Hellwig
2021-01-28 18:14   ` Christoph Hellwig
2021-01-28 18:14 ` [PATCH 12/13] module: remove EXPORT_SYMBOL_GPL_FUTURE Christoph Hellwig
2021-01-28 18:14   ` Christoph Hellwig
2021-01-28 18:14 ` [PATCH 13/13] module: remove EXPORT_UNUSED_SYMBOL* Christoph Hellwig
2021-02-02 12:13 module loader dead code removal and cleanups v3 Christoph Hellwig
2021-02-02 12:13 ` [PATCH 04/13] module: use RCU to synchronize find_module Christoph Hellwig
2021-02-02 12:13   ` Christoph Hellwig

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