On Wed, Jun 11, 2014 at 04:39:42PM -0400, Pranith Kumar wrote:
> kernel/rcu/tree.c:3435:21: warning: incorrect type in argument 1 (different
> modifiers)
> kernel/rcu/tree.c:3435:21: expected int ( *threadfn )( ... )
> kernel/rcu/tree.c:3435:21: got int ( static [toplevel] [noreturn]
> *<noident> )( ... )
>
> by removing __noreturn attribute and adding unreachable() as suggested on the
> mailing list: http://www.kernelhub.org/?p=2&msg=436683
>
> Signed-off-by: Pranith Kumar <bobby.pr...@gmail.com>
No, we should not do this. And the mailing list post you point to seems
to explicitly recommend using noreturn rather than unreachable.
If sparse doesn't understand this, that's a bug in sparse, not in the
kernel. Sparse needs to understand that it's OK to drop noreturn from a
function pointer type, just not OK to add it.
Rationale: If you call a noreturn function through a non-noreturn
function pointer, you might end up with unnecessary cleanup code, but
the call will work. If you call a non-noreturn function through a
noreturn function pointer, the caller will not expect a return, and may
crash; *that* should require a cast.
> kernel/rcu/tree.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 9ab84d3..6029a2e 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1689,7 +1689,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
> /*
> * Body of kthread that handles grace periods.
> */
> -static int __noreturn rcu_gp_kthread(void *arg)
> +static int rcu_gp_kthread(void *arg)
> {
> int fqs_state;
> int gf;
> @@ -1777,6 +1777,9 @@ static int __noreturn rcu_gp_kthread(void *arg)
> /* Handle grace-period end. */
> rcu_gp_cleanup(rsp);
> }
> +
> + unreachable();
> + return 0;
> }
>
> /*
> --
> 1.9.1
>
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