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

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Message-Id: <20210128181421.2279-5-hch@lst.de>
Date:   Thu, 28 Jan 2021 19:14:12 +0100
From:   Christoph Hellwig <hch@....de>
To:     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>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        dri-devel@...ts.freedesktop.org, live-patching@...r.kernel.org,
        linux-kbuild@...r.kernel.org
Subject: [PATCH 04/13] module: use RCU to synchronize find_module

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.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 include/linux/module.h      | 2 +-
 kernel/livepatch/core.c     | 5 +++--
 kernel/module.c             | 1 -
 kernel/trace/trace_kprobe.c | 4 ++--
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 7a0bcb5b1ffccd..a64aa84d1b182c 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -586,7 +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. */
+/* Search for module by name: must be in a RCU-sched critical section. */
 struct module *find_module(const char *name);
 
 struct symsearch {
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index f76fdb9255323d..262cd9b003b9f0 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -19,6 +19,7 @@
 #include <linux/moduleloader.h>
 #include <linux/completion.h>
 #include <linux/memory.h>
+#include <linux/rcupdate.h>
 #include <asm/cacheflush.h>
 #include "core.h"
 #include "patch.h"
@@ -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)
 		obj->mod = mod;
 
-	mutex_unlock(&module_mutex);
+	rcu_read_unlock_sched();
 }
 
 static bool klp_initialized(void)
diff --git a/kernel/module.c b/kernel/module.c
index 981302f616b411..6772fb2680eb3e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -668,7 +668,6 @@ static struct module *find_module_all(const char *name, size_t len,
 
 struct module *find_module(const char *name)
 {
-	module_assert_mutex();
 	return find_module_all(name, strlen(name), false);
 }
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index e6fba1798771b4..3137992baa5e7a 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -124,9 +124,9 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
 	if (!p)
 		return true;
 	*p = '\0';
-	mutex_lock(&module_mutex);
+	rcu_read_lock_sched();
 	ret = !!find_module(tk->symbol);
-	mutex_unlock(&module_mutex);
+	rcu_read_unlock_sched();
 	*p = ':';
 
 	return ret;
-- 
2.29.2