From: Jessica Yu <jeyu@kernel.org>
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>,
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 13:10:37 +0100 [thread overview]
Message-ID: <YBfvvdna9pSeu+1g@gunter> (raw)
In-Reply-To: <alpine.LSU.2.21.2101291626080.22237@pobox.suse.cz>
+++ Miroslav Benes [29/01/21 16:29 +0100]:
>On Thu, 28 Jan 2021, Christoph Hellwig wrote:
>
>> Allow for a RCU-sched critical section around find_module, following
>> the lower level find_module_all helper, and switch the two callers
>> outside of module.c to use such a RCU-sched critical section instead
>> of module_mutex.
>
>That's a nice idea.
>
>> @@ -57,7 +58,7 @@ static void klp_find_object_module(struct klp_object *obj)
>> if (!klp_is_module(obj))
>> return;
>>
>> - 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.
Same here :-) I had to double check the RCU documentation. For our
modules list case I believe the rcu list API should take care of that
for us. Worth noting is this snippet from Documentation/RCU/whatisRCU.txt:
rcu_dereference() is typically used indirectly, via the _rcu
list-manipulation primitives, such as list_for_each_entry_rcu()
next prev parent reply other threads:[~2021-02-01 12:11 UTC|newest]
Thread overview: 22+ 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 ` [PATCH 01/13] powerpc/powernv: remove get_cxl_module Christoph Hellwig
2021-01-28 18:14 ` [PATCH 03/13] module: unexport find_module and module_mutex Christoph Hellwig
2021-01-28 18:14 ` [PATCH 04/13] module: use RCU to synchronize find_module Christoph Hellwig
2021-01-28 20:50 ` Thiago Jung Bauermann
2021-01-29 5:10 ` Christoph Hellwig
2021-01-29 21:29 ` Thiago Jung Bauermann
[not found] ` <alpine.LSU.2.21.2101291626080.22237@pobox.suse.cz>
2021-02-01 11:46 ` Christoph Hellwig
2021-02-01 12:10 ` Jessica Yu [this message]
2021-02-01 13:16 ` Miroslav Benes
2021-01-28 18:14 ` [PATCH 07/13] module: mark module_mutex static 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 ` [PATCH 11/13] module: move struct symsearch to module.c Christoph Hellwig
2021-01-28 18:14 ` [PATCH 12/13] module: remove EXPORT_SYMBOL_GPL_FUTURE Christoph Hellwig
[not found] ` <20210128181421.2279-6-hch@lst.de>
[not found] ` <YBPYyEvesLMrRtZM@alley>
2021-02-01 11:47 ` [PATCH 05/13] kallsyms: refactor {,module_}kallsyms_on_each_symbol Christoph Hellwig
2021-02-01 13:37 ` Miroslav Benes
2021-02-01 16:28 ` Christoph Hellwig
2021-02-02 10:45 ` Miroslav Benes
2021-02-01 14:02 ` Miroslav Benes
[not found] ` <20210128181421.2279-3-hch@lst.de>
2021-02-03 10:34 ` [PATCH 02/13] drm: remove drm_fb_helper_modinit Daniel Vetter
2021-02-03 10:49 ` 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
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