bitops: Fix shift overflow in GENMASK macros

On some 32 bits architectures, including x86, GENMASK(31, 0) returns 0
instead of the expected ~0UL.

This is the same on some 64 bits architectures with GENMASK_ULL(63, 0).

This is due to an overflow in the shift operand, 1 << 32 for GENMASK,
1 << 64 for GENMASK_ULL.

Reported-by: Eric Paire <[email protected]>
Suggested-by: Rasmus Villemoes <[email protected]>
Signed-off-by: Maxime Coquelin <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: <[email protected]> # v3.13+
Cc: [email protected]
Cc: [email protected]
Cc: John Sullivan <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Theodore Ts'o <[email protected]>
Fixes: 10ef6b0dffe4 ("bitops: Introduce a more generic BITMASK macro")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 5 insertions, 2 deletions

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index be5fd38bd5a0..5d858e02997f 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -18,8 +18,11 @@
  * position @h. For example
  * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
  */
-#define GENMASK(h, l)		(((U32_C(1) << ((h) - (l) + 1)) - 1) << (l))
-#define GENMASK_ULL(h, l)	(((U64_C(1) << ((h) - (l) + 1)) - 1) << (l))
+#define GENMASK(h, l) \
+	(((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
+
+#define GENMASK_ULL(h, l) \
+	(((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
 
 extern unsigned int __sw_hweight8(unsigned int w);
 extern unsigned int __sw_hweight16(unsigned int w);