locking, compiler.h: Cast away attributes in the WRITE_ONCE() magic

The kernel build bot showed a new warning triggered by commit:

  76695af20c01 ("locking, arch: use WRITE_ONCE()/READ_ONCE() in smp_store_release()/smp_load_acquire()")

because 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_ONCE().

(And as this now gets too long, also split the macro into multiple lines.)

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1438674948-38310-2-git-send-email-borntraeger@de.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index e08a6ae..c836eb2 100644 (file)
--- 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;                                      \
+})
 
 /**
  * READ_ONCE_CTRL - Read a value heading a control dependency