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From: Jessica Yu <jeyu@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: 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>, Miroslav Benes <mbenes@suse.cz>,
	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] livepatch: move klp_find_object_module to module.c
Date: Tue, 26 Jan 2021 15:25:16 +0100	[thread overview]
Message-ID: <YBAmTAsT3S01kU1x@gunter> (raw)
In-Reply-To: <20210121074959.313333-5-hch@lst.de>

+++ Christoph Hellwig [21/01/21 08:49 +0100]:
>To uncouple the livepatch code from module loader internals move a
>slightly refactored version of klp_find_object_module to module.c
>This allows to mark find_module static and removes one of the last
>users of module_mutex outside of module.c.
>
>Signed-off-by: Christoph Hellwig <hch@lst.de>
>---
> include/linux/module.h  |  3 +--
> kernel/livepatch/core.c | 39 +++++++++++++--------------------------
> kernel/module.c         | 17 ++++++++++++++++-
> 3 files changed, 30 insertions(+), 29 deletions(-)
>
>diff --git a/include/linux/module.h b/include/linux/module.h
>index b4654f8a408134..8588482bde4116 100644
>--- a/include/linux/module.h
>+++ b/include/linux/module.h
>@@ -586,8 +586,7 @@ static inline bool within_module(unsigned long addr, const struct module *mod)
> 	return within_module_init(addr, mod) || within_module_core(addr, mod);
> }
>
>-/* Search for module by name: must hold module_mutex. */
>-struct module *find_module(const char *name);
>+struct module *find_klp_module(const char *name);
>
> /* Check if a module is loaded. */
> bool module_loaded(const char *name);
>diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
>index a7f625dc24add3..878759baadd81c 100644
>--- a/kernel/livepatch/core.c
>+++ b/kernel/livepatch/core.c
>@@ -49,30 +49,6 @@ static bool klp_is_module(struct klp_object *obj)
> 	return obj->name;
> }
>
>-/* sets obj->mod if object is not vmlinux and module is found */
>-static void klp_find_object_module(struct klp_object *obj)
>-{
>-	struct module *mod;
>-
>-	mutex_lock(&module_mutex);
>-	/*
>-	 * We do not want to block removal of patched modules and therefore
>-	 * we do not take a reference here. The patches are removed by
>-	 * klp_module_going() instead.
>-	 */
>-	mod = find_module(obj->name);
>-	/*
>-	 * Do not mess work of klp_module_coming() and klp_module_going().
>-	 * Note that the patch might still be needed before klp_module_going()
>-	 * is called. Module functions can be called even in the GOING state
>-	 * until mod->exit() finishes. This is especially important for
>-	 * patches that modify semantic of the functions.
>-	 */
>-	if (mod && mod->klp_alive)
>-		obj->mod = mod;
>-	mutex_unlock(&module_mutex);
>-}

Hmm, I am not a huge fan of moving more livepatch code into module.c, I
wonder if we can keep them separate.

Why not have module_is_loaded() kill two birds with one stone? That
is, just have it return a module pointer to signify that the module is
loaded, NULL if not. Then we don't need an extra find_klp_module()
function just to call find_module() and return a pointer, as
module_is_loaded() can just do that for us.

As for the mod->klp_alive check, I believe this function
(klp_find_object_module()) is called with klp_mutex held, and
mod->klp_alive is only modified under klp_mutex. Also, if klp_alive is
true, the module is at least COMING and cannot be GOING until it
acquires the klp_mutex again in klp_module_going(). So does that hunk
really need to be under module_mutex? It has been a long time since
I've looked at livepatch code so it would be great if someone could
double check.

Jessica

  parent reply	other threads:[~2021-01-26 14:29 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-21  7:49 module loader dead code removal and cleanusp Christoph Hellwig
2021-01-21  7:49 ` [PATCH 01/13] powerpc/powernv: remove get_cxl_module Christoph Hellwig
2021-01-21  9:09   ` Andrew Donnellan
2021-01-21  7:49 ` [PATCH 02/13] module: add a module_loaded helper Christoph Hellwig
2021-01-21 10:00   ` Christophe Leroy
2021-01-21 17:11     ` Christoph Hellwig
2021-01-21 17:44       ` David Laight
2021-01-21  7:49 ` [PATCH 03/13] livepatch: refactor klp_init_object Christoph Hellwig
2021-01-27 12:58   ` Petr Mladek
2021-01-28 16:22     ` Christoph Hellwig
2021-01-28 16:24       ` Christoph Hellwig
2021-01-21  7:49 ` [PATCH 04/13] livepatch: move klp_find_object_module to module.c Christoph Hellwig
2021-01-21 21:45   ` Josh Poimboeuf
2021-01-26 14:25   ` Jessica Yu [this message]
2021-01-27 11:55     ` Petr Mladek
2021-01-21  7:49 ` [PATCH 05/13] kallsyms: refactor {,module_}kallsyms_on_each_symbol Christoph Hellwig
2021-01-21  7:49 ` [PATCH 06/13] kallsyms: only build {,module_}kallsyms_on_each_symbol when required Christoph Hellwig
2021-01-21  7:49 ` [PATCH 07/13] module: mark module_mutex static Christoph Hellwig
2021-01-21  7:49 ` [PATCH 08/13] drm: remove drm_fb_helper_modinit Christoph Hellwig
2021-01-21  8:25   ` Daniel Vetter
2021-01-21  8:28     ` Christoph Hellwig
2021-01-21  8:39       ` Daniel Vetter
2021-01-21  7:49 ` [PATCH 09/13] module: remove each_symbol_in_section Christoph Hellwig
2021-01-21  7:49 ` [PATCH 10/13] module: merge each_symbol_section into find_symbol Christoph Hellwig
2021-01-21  7:49 ` [PATCH 11/13] module: pass struct find_symbol_args to find_symbol Christoph Hellwig
2021-01-21  7:49 ` [PATCH 12/13] module: remove EXPORT_SYMBOL_GPL_FUTURE Christoph Hellwig
2021-01-21  7:49 ` [PATCH 13/13] module: remove EXPORY_UNUSED_SYMBOL* Christoph Hellwig
2021-01-27 13:49   ` Jessica Yu
2021-01-28 16:09     ` Christoph Hellwig

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