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    SubjectRe: [PATCH 1/2] Make the module 'usage' lists be two-way
    On Mon, May 31, 2010 at 01:16:23PM -0700, Linus Torvalds wrote:
    >From: Linus Torvalds <>
    >Date: Mon, 31 May 2010 12:19:37 -0700
    >Subject: [PATCH 1/2] Make the module 'usage' lists be two-way
    >When adding a module that depends on another one, we used to create a
    >one-way list of "modules_which_use_me", so that module unloading could
    >see who needs a module.
    >It's actually quite simple to make that list go both ways: so that we
    >not only can see "who uses me", but also see a list of modules that are
    >"used by me".
    >In fact, we always wanted that list in "module_unload_free()": when we
    >unload a module, we want to also release all the other modules that are
    >used by that module. But because we didn't have that list, we used to
    >first iterate over all modules, and then iterate over each "used by me"
    >list of that module.
    >By making the list two-way, we simplify module_unload_free(), and it
    >allows for some trivial fixes later too.
    >Signed-off-by: Linus Torvalds <>

    Hi, Linus,

    > /* Clear the unload stuff of the module. */
    > static void module_unload_free(struct module *mod)
    > {
    >- struct module *i;
    >+ struct module_use *use, *tmp;
    >- list_for_each_entry(i, &modules, list) {
    >- struct module_use *use;
    >- list_for_each_entry(use, &i->modules_which_use_me, list) {
    >- if (use->module_which_uses == mod) {
    >- DEBUGP("%s unusing %s\n", mod->name, i->name);
    >- module_put(i);
    >- list_del(&use->list);
    >- kfree(use);
    >- sysfs_remove_link(i->holders_dir, mod->name);
    >- /* There can be at most one match. */
    >- break;
    >- }
    >- }
    >+ list_for_each_entry_safe(use, tmp, &mod->target_list, target_list) {
    >+ struct module *i = use->target;
    >+ DEBUGP("%s unusing %s\n", mod->name, i->name);
    >+ module_put(i);
    >+ list_del(&use->source_list);
    >+ list_del(&use->target_list);
    >+ kfree(use);
    >+ sysfs_remove_link(i->holders_dir, mod->name);

    I think it's nice to have a remove_module_usage() here, since we already
    have add_module_usage().


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