linux-kernel - [RFC 10/12] module: avoid allocation if module is already present and ready

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Message-Id: <20230311051712.4095040-11-mcgrof@kernel.org>
Date:   Fri, 10 Mar 2023 21:17:10 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
        pmladek@...e.com, david@...hat.com, petr.pavlu@...e.com,
        prarit@...hat.com
Cc:     christophe.leroy@...roup.eu, song@...nel.org, mcgrof@...nel.org,
        torvalds@...ux-foundation.org
Subject: [RFC 10/12] module: avoid allocation if module is already present and ready

load_module() will allocate a struct module before even checking
if the module is already loaded. This can create unecessary memory
pressure since we can easily just check if the module is already
present early with the copy of the module information from userspace
after we've validated it a bit.

This can only be an issue if a system is getting hammered with userspace
loading modules. Note that there are two ways to load modules, one is
auto-loading in-kernel and that pings back to userspace to just call
modprobe. Then userspace itself *is* supposed to check if a module
is present before loading it. But we're observing situations where
tons of the same module are in effect being loaded. In that situation
we can end up allocating memory for module requests which after
allocating memory will fail to load.

To avoid memory pressure for such stupid cases put a stop gap for them.

Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
---
 kernel/module/main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index e24323e2c499..909454f9616e 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2713,6 +2713,10 @@ static int early_mod_check(struct load_info *info, int flags)
 	if (err)
 		return err;

+	err = module_patient_check_exists(info->mod->name);
+	if (err)
+		return err;
+
 	return 0;
 }

-- 
2.39.1