linux-kernel - Re: [GIT PULL] SafeSetID LSM changes for 5.4

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Date:   Mon, 21 Oct 2019 08:58:11 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Micah Morton <mortonm@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        Bart Van Assche <bart.vanassche@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [GIT PULL] SafeSetID LSM changes for 5.4


* Paul E. McKenney <paulmck@...nel.org> wrote:

> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -383,20 +383,22 @@ do {									      \
>  } while (0)
>  
>  /**
> - * rcu_swap_protected() - swap an RCU and a regular pointer
> - * @rcu_ptr: RCU pointer
> + * rcu_replace() - replace an RCU pointer, returning its old value
> + * @rcu_ptr: RCU pointer, whose old value is returned
>   * @ptr: regular pointer
> - * @c: the conditions under which the dereference will take place
> + * @c: the lockdep conditions under which the dereference will take place
>   *
> - * Perform swap(@rcu_ptr, @ptr) where @rcu_ptr is an RCU-annotated pointer and
> - * @c is the argument that is passed to the rcu_dereference_protected() call
> - * used to read that pointer.
> + * Perform a replacement, where @rcu_ptr is an RCU-annotated
> + * pointer and @c is the lockdep argument that is passed to the
> + * rcu_dereference_protected() call used to read that pointer.  The old
> + * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
>   */
> -#define rcu_swap_protected(rcu_ptr, ptr, c) do {			\
> +#define rcu_replace(rcu_ptr, ptr, c)					\
> +({									\
>  	typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c));	\
>  	rcu_assign_pointer((rcu_ptr), (ptr));				\
> -	(ptr) = __tmp;							\
> -} while (0)
> +	__tmp;								\
> +})

One small suggestion, would it make sense to name it "rcu_replace_pointer()"?

This would make it fit into the pointer handling family of RCU functions: 
rcu_assign_pointer(), rcu_access_pointer(), RCU_INIT_POINTER() et al?

rcu_swap() would also look a bit weird if used in MM code. ;-)

Thanks,

	Ingo