Commit ba33034f authored Aug 04, 2015 by Christian Borntraeger Committed by Ingo Molnar Aug 12, 2015

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



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

  76695af2 ("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>

parent f52609fd

include/linux/compiler.h

+6 −1

Original line number	Diff line number	Diff line
		@@ -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

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