Messages in this thread Patch in this message | | | Date | Tue, 9 Jul 2019 18:10:39 +0200 | From | Jessica Yu <> | Subject | Re: [PATCH v2] module: add usage links when calling ref_module func |
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+++ Zhiqiang Liu [03/07/19 10:09 +0800]: >From: Zhiqiang Liu <liuzhiqiang26@huawei.com> > >Users can call ref_module func in their modules to construct >relationships with other modules. However, the holders >'/sys/module/<mod-name>/holders' of the target module donot include >the users` module. So lsmod command misses detailed info of 'Used by'. > >When load module, the process is given as follows, >load_module() > -> mod_sysfs_setup() > -> add_usage_links > -> do_init_module > -> mod->init() > >add_usage_links func creates holders of target modules linking to >this module. If ref_module is called in mod->init() func, the usage >links cannot be added. > >Here, we will add usage link of a to b's holder_dir. > >V1->V2: >- remove incorrect Fixes tag >- fix error handling of sysfs_create_link as suggested by Jessica Yu > >Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com> >Suggested-by: Jessica Yu <jeyu@kernel.org> >Reviewed-by: Kang Zhou <zhoukang7@huawei.com> >--- > 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). > */ >-static int add_module_usage(struct module *a, struct module *b) >+static struct module_use *add_module_usage(struct module *a, struct module *b) > { > struct module_use *use; > > pr_debug("Allocating new usage for %s.\n", a->name); > use = kmalloc(sizeof(*use), GFP_ATOMIC); > if (!use) >- return -ENOMEM; >+ return NULL; > > use->source = a; > use->target = b; > list_add(&use->source_list, &b->source_list); > list_add(&use->target_list, &a->target_list); >- return 0; >+ return use; > } > > /* 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.
> if (err) { > module_put(b); >+ list_del(&use->source_list); >+ list_del(&use->target_list); >+ kfree(use); > return err; > } > return 0; >-- >2.19.1 >
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