Patch "module: use RCU to synchronize find_module" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    module: use RCU to synchronize find_module

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     module-use-rcu-to-synchronize-find_module.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 9c4174bb60699f54ee7f2c1dca8a4db4b5f0a022
Author: Christoph Hellwig <hch@xxxxxx>
Date:   Tue Feb 2 13:13:25 2021 +0100

    module: use RCU to synchronize find_module
    
    [ Upstream commit a006050575745ca2be25118b90f1c37f454ac542 ]
    
    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.
    
    Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
    Acked-by: Miroslav Benes <mbenes@xxxxxxx>
    Signed-off-by: Christoph Hellwig <hch@xxxxxx>
    Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/module.h b/include/linux/module.h
index 6264617bab4d4..86fae5d1c0e39 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -582,7 +582,7 @@ 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 f5faf935c2d8f..e660ea4f90a28 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 c0e51ffe26f0a..1f9f6133c30ef 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -641,7 +641,6 @@ 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 7183572898998..5453af26ff764 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;