linux-kernel - Re: [PATCH] modules: elide param_lock if !CONFIG

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Message-ID: <CALZtOND_-LahkJE5pD6eQOusT42M4-9ECKZ1cD+F_dPK4CVX8A@mail.gmail.com>
Date:	Thu, 25 Jun 2015 17:34:31 -0400
From:	Dan Streetman <ddstreet@...e.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] modules: elide param_lock if !CONFIG_SYSFS

On Thu, Jun 25, 2015 at 5:18 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> Dan Streetman <ddstreet@...e.org> writes:
>> Only include the built-in and per-module param_lock, and corresponding
>> lock/unlock functions, if sysfs is enabled.  If there is no sysfs there
>> is no need for locking kernel params.
>>
>> This fixes a build break when CONFIG_SYSFS is not enabled, introduced
>> by commit b51d23e.
>
> This doesn't even come close to applying to my tree?

sorry, I had the !CONFIG_MODULES patch in my tree also, so this was on
top of that one:
https://lkml.org/lkml/2015/6/24/550

I can resend that one, on top of this one, or you can fix it up.

Sorry for not getting it right the first time ;-)

>
> I've fixed it like so, and tested it compiles both with and without
> SYSFS.
>
> Subject: param: fix module param locks when !CONFIG_SYSFS.
>
> As Dan Streetman points out, the entire point of locking for is to
> stop sysfs accesses, so they're elided entirely in the !SYSFS case.
>
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index abaecf1a63df..237bce382e32 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -240,7 +240,9 @@ struct module {
>         unsigned int num_syms;
>
>         /* Kernel parameters. */
> +#ifdef CONFIG_SYSFS
>         struct mutex param_lock;
> +#endif
>         struct kernel_param *kp;
>         unsigned int num_kp;
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 1dcf09f214fa..c19b2c50b317 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1820,6 +1820,10 @@ static void mod_sysfs_fini(struct module *mod)
>         mod_kobject_put(mod);
>  }
>
> +static void init_param_lock(struct module *mod)
> +{
> +       mutex_init(&mod->param_lock);
> +}
>  #else /* !CONFIG_SYSFS */
>
>  static int mod_sysfs_setup(struct module *mod,
> @@ -1842,6 +1846,9 @@ static void del_usage_links(struct module *mod)
>  {
>  }
>
> +static void init_param_lock(struct module *mod)
> +{
> +}
>  #endif /* CONFIG_SYSFS */
>
>  static void mod_sysfs_teardown(struct module *mod)
> @@ -3442,7 +3449,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
>         if (err)
>                 goto unlink_mod;
>
> -       mutex_init(&mod->param_lock);
> +       init_param_lock(mod);

oops, i missed fixing this up, when I tested with allnoconfig this
wasn't built due to CONFIG_MODULES=n.  I should have built only with
syfs=n :(

>
>         /* Now we've got everything in the final locations, we can
>          * find optional sections. */
> diff --git a/kernel/params.c b/kernel/params.c
> index 8890d0b8dffc..faa461c16f12 100644
> --- a/kernel/params.c
> +++ b/kernel/params.c
> @@ -25,12 +25,22 @@
>  #include <linux/slab.h>
>  #include <linux/ctype.h>
>
> +#ifdef CONFIG_SYSFS
>  /* Protects all built-in parameters, modules use their own param_lock */
>  static DEFINE_MUTEX(param_lock);
>
>  /* Use the module's mutex, or if built-in use the built-in mutex */
>  #define KPARAM_MUTEX(mod)      ((mod) ? &(mod)->param_lock : &param_lock)
> -#define KPARAM_IS_LOCKED(mod)  mutex_is_locked(KPARAM_MUTEX(mod))
> +
> +static inline void check_kparam_locked(struct module *mod)
> +{
> +       BUG_ON(!mutex_is_locked(KPARAM_MUTEX(mod)));
> +}
> +#else
> +static inline void check_kparam_locked(struct module *mod)
> +{
> +}
> +#endif /* !CONFIG_SYSFS */
>
>  /* This just allows us to keep track of which parameters are kmalloced. */
>  struct kmalloced_param {
> @@ -459,7 +469,7 @@ static int param_array(struct module *mod,
>                 /* nul-terminate and parse */
>                 save = val[len];
>                 ((char *)val)[len] = '\0';
> -               BUG_ON(!KPARAM_IS_LOCKED(mod));
> +               check_kparam_locked(mod);
>                 ret = set(val, &kp);
>
>                 if (ret != 0)
> @@ -496,7 +506,7 @@ static int param_array_get(char *buffer, const struct kernel_param *kp)
>                 if (i)
>                         buffer[off++] = ',';
>                 p.arg = arr->elem + arr->elemsize * i;
> -               BUG_ON(!KPARAM_IS_LOCKED(p.mod));
> +               check_kparam_locked(p.mod);
>                 ret = arr->ops->get(buffer + off, &p);
>                 if (ret < 0)
>                         return ret;
> @@ -616,6 +626,7 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
>  #define __modinit __init
>  #endif
>
> +#ifdef CONFIG_SYSFS
>  void kernel_param_lock(struct module *mod)
>  {
>         mutex_lock(KPARAM_MUTEX(mod));
> @@ -626,7 +637,6 @@ void kernel_param_unlock(struct module *mod)
>         mutex_unlock(KPARAM_MUTEX(mod));
>  }
>
> -#ifdef CONFIG_SYSFS
>  EXPORT_SYMBOL(kernel_param_lock);
>  EXPORT_SYMBOL(kernel_param_unlock);
>
--
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