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    Subject[PATCH 7/7] module: avoid exporting module_mutex
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    drm_fb_helper_modinit() calls find_module() which only
    needs rcu_read_lock_sched().

    The rest seems still have to hold module_mutex to prevent
    module insertion/deletion. Instead of exporting module_mutex
    for them, export two functions lock_modules()/unlock_modules()
    and hide module_mutex.

    Cc: Eric Dumazet <eric.dumazet@gmail.com>
    Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
    ---
    drivers/gpu/drm/drm_fb_helper.c | 4 ++--
    include/linux/module.h | 3 ++-
    kernel/kprobes.c | 4 ++--
    kernel/module.c | 24 ++++++++++++++++++------
    4 files changed, 24 insertions(+), 11 deletions(-)

    diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
    index aada26f..a3aee0e 100644
    --- a/drivers/gpu/drm/drm_fb_helper.c
    +++ b/drivers/gpu/drm/drm_fb_helper.c
    @@ -1451,9 +1451,9 @@ static int __init drm_fb_helper_modinit(void)
    const char *name = "fbcon";
    struct module *fbcon;

    - mutex_lock(&module_mutex);
    + rcu_read_lock_sched();
    fbcon = find_module(name);
    - mutex_unlock(&module_mutex);
    + rcu_read_unlock_sched();

    if (!fbcon)
    request_module_nowait(name);
    diff --git a/include/linux/module.h b/include/linux/module.h
    index 4598bf0..5cf6428 100644
    --- a/include/linux/module.h
    +++ b/include/linux/module.h
    @@ -374,7 +374,8 @@ struct module
    #define MODULE_ARCH_INIT {}
    #endif

    -extern struct mutex module_mutex;
    +extern void lock_modules(void);
    +extern void unlock_modules(void);

    /* FIXME: It'd be nice to isolate modules during init, too, so they
    aren't used before they (may) fail. But presently too much code
    diff --git a/kernel/kprobes.c b/kernel/kprobes.c
    index c62b854..0670fb1 100644
    --- a/kernel/kprobes.c
    +++ b/kernel/kprobes.c
    @@ -562,7 +562,7 @@ static __kprobes void kprobe_optimizer(struct work_struct *work)
    LIST_HEAD(free_list);

    /* Lock modules while optimizing kprobes */
    - mutex_lock(&module_mutex);
    + lock_modules();
    mutex_lock(&kprobe_mutex);

    /*
    @@ -587,7 +587,7 @@ static __kprobes void kprobe_optimizer(struct work_struct *work)
    do_free_cleaned_kprobes(&free_list);

    mutex_unlock(&kprobe_mutex);
    - mutex_unlock(&module_mutex);
    + unlock_modules();

    /* Step 5: Kick optimizer again if needed */
    if (!list_empty(&optimizing_list) || !list_empty(&unoptimizing_list))
    diff --git a/kernel/module.c b/kernel/module.c
    index 2e7a5c5..b60f882 100644
    --- a/kernel/module.c
    +++ b/kernel/module.c
    @@ -95,8 +95,20 @@
    * 2) module_use links,
    * 3) module_addr_min/module_addr_max.
    * (delete uses stop_machine/add uses RCU list operations). */
    -DEFINE_MUTEX(module_mutex);
    -EXPORT_SYMBOL_GPL(module_mutex);
    +static DEFINE_MUTEX(module_mutex);
    +
    +void lock_modules(void)
    +{
    + mutex_lock(&module_mutex);
    +}
    +EXPORT_SYMBOL(lock_modules);
    +
    +void unlock_modules(void)
    +{
    + mutex_unlock(&module_mutex);
    +}
    +EXPORT_SYMBOL(unlock_modules);
    +
    static LIST_HEAD(modules);
    #ifdef CONFIG_KGDB_KDB
    struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
    @@ -1715,7 +1727,7 @@ void set_all_modules_text_rw(void)
    {
    struct module *mod;

    - mutex_lock(&module_mutex);
    + lock_modules();
    list_for_each_entry_rcu(mod, &modules, list) {
    if ((mod->module_core) && (mod->core_text_size)) {
    set_page_attributes(mod->module_core,
    @@ -1728,7 +1740,7 @@ void set_all_modules_text_rw(void)
    set_memory_rw);
    }
    }
    - mutex_unlock(&module_mutex);
    + unlock_modules();
    }

    /* Iterate through all modules and set each module's text as RO */
    @@ -1736,7 +1748,7 @@ void set_all_modules_text_ro(void)
    {
    struct module *mod;

    - mutex_lock(&module_mutex);
    + lock_modules();
    list_for_each_entry_rcu(mod, &modules, list) {
    if ((mod->module_core) && (mod->core_text_size)) {
    set_page_attributes(mod->module_core,
    @@ -1749,7 +1761,7 @@ void set_all_modules_text_ro(void)
    set_memory_ro);
    }
    }
    - mutex_unlock(&module_mutex);
    + unlock_modules();
    }
    #else
    static inline void set_section_ro_nx(void *base, unsigned long text_size, unsigned long ro_size, unsigned long total_size) { }
    --
    1.7.7.6


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