linux-kernel - Re: [RFC PATCH 4/5] kernel/rcu/tree.c:3435 fix a sparse warning

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Message-ID: <CAJhHMCC5dAvKZFmWnaDqS6zG+WeH-YT7qCTPypDEuEuYOGy_sw@mail.gmail.com>
Date:	Wed, 11 Jun 2014 21:37:22 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 4/5] kernel/rcu/tree.c:3435 fix a sparse warning

On Wed, Jun 11, 2014 at 5:25 PM,  <josh@...htriplett.org> wrote:
> 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.prani@...il.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.
>

Yes, I understand the rationale. I think this should be fixed in
sparse. Please drop this patch.

Thanks!
-- 
Pranith
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