On Tue, Aug 04, 2015 at 09:55:48AM +0200, Christian Borntraeger wrote:
> kernel build bot showed a warning triggered by commit
> 76695af20c01 ("locking, arch: use WRITE_ONCE()/READ_ONCE() in
> smp_store_release()/smp_load_acquire()"). Turns out that sparse
> does not like WRITE_ONCE accessing elements from the (sparse)
> rcu address space.
>
> fs/afs/inode.c:448:9: sparse: incorrect type in initializer (different
> address spaces)
> fs/afs/inode.c:448:9: expected struct afs_permits *__val
> fs/afs/inode.c:448:9: got void [noderef] <asn:4>*<noident>
>
> Solution is to force cast away the sparse attributes for the initializer
> of the union in WRITE_SAME. As this now gets too long, lets split
WRITE_ONCE, right?
> the macro.
>
> Signed-off-by: Christian Borntraeger <[email protected]>
> ---
> include/linux/compiler.h | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index e08a6ae..c836eb2 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -252,7 +252,12 @@ static __always_inline void __write_once_size(volatile
> void *p, void *res, int s
> ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x),
> __u.__c, sizeof(x)); __u.__val; })
>
> #define WRITE_ONCE(x, val) \
> - ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) };
> __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
> +({ \
> + union { typeof(x) __val; char __c[1]; } __u = \
> + { .__val = (__force typeof(x)) (val) }; \
> + __write_once_size(&(x), __u.__c, sizeof(x)); \
> + __u.__val; \
> +})
Thanks!
READ_ONCE() doesn't have a similar problem because it only has the one
input type, which automagically becomes the output type, right?
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