Re: [PATCH v2] module: add usage links when calling ref_module func

From: Jessica Yu
Date: Thu Jul 11 2019 - 05:17:30 EST

+++ Zhiqiang Liu [11/07/19 14:03 +0800]:

On 2019/7/10 0:10, Jessica Yu wrote:
+++ Zhiqiang Liu [03/07/19 10:09 +0800]:
From: Zhiqiang Liu <liuzhiqiang26@xxxxxxxxxx

- remove incorrect Fixes tag
- fix error handling of sysfs_create_link as suggested by Jessica Yu

Signed-off-by: Zhiqiang Liu <liuzhiqiang26@xxxxxxxxxx>
Suggested-by: Jessica Yu <jeyu@xxxxxxxxxx>
Reviewed-by: Kang Zhou <zhoukang7@xxxxxxxxxx>
kernel/module.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 80c7c09584cf..672abce2222c 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -837,25 +837,26 @@ static int already_uses(struct module *a, struct module *b)
 *    'b' can walk the list to see who sourced them), and of 'a'
 *    targets (so 'a' can see what modules it targets).
/* Module a uses b: caller needs module_mutex() */
int ref_module(struct module *a, struct module *b)
+    struct module_use *use;
    int err;

    if (b == NULL || already_uses(a, b))
@@ -866,9 +867,18 @@ int ref_module(struct module *a, struct module *b)
    if (err)
        return err;

-    err = add_module_usage(a, b);
+    use = add_module_usage(a, b);
+    if (!use) {
+        module_put(b);
+        return -ENOMEM;
+    }
+    err = sysfs_create_link(b->holders_dir, &a->mkobj.kobj, a->name);

Sigh. This ultimately doesn't work because in load_module(), we use
ref_module() in resolve_symbol(), and mod->mkobj.kobj doesn't get
initialized until mod_sysfs_init(), which happens much later in
load_module(). So what happens is that the ref_module(mod, owner) call
in resolve_symbol() returns an error because sysfs_create_link() fails here.
We could *maybe* move sysfs initialization earlier in load_module()
but that is an entirely untested idea and I would need to think about
that more.

Thank you for the reply.
I have tested the patch through livepatch. Maybe I miss somethings.
I will rewrite the patch and test it entirely before sending the v3 patch.

Thanks Zhiqiang. A boot test and testing loading modules with
dependencies would be really appreciated.