linux-kernel - [PATCH] asm-generic: fix -Wtype-limits compiler warnings

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Date:   Tue, 23 Jul 2019 16:49:46 -0400
From:   Qian Cai <cai@....pw>
To:     akpm@...ux-foundation.org
Cc:     davem@...emloft.net, arnd@...db.de, dhowells@...hat.com,
        jakub@...hat.com, ndesaulniers@...gle.com, morbo@...gle.com,
        jyknight@...gle.com, natechancellor@...il.com,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        Qian Cai <cai@....pw>
Subject: [PATCH] asm-generic: fix -Wtype-limits compiler warnings

The commit d66acc39c7ce ("bitops: Optimise get_order()") introduced a
compilation warning because "rx_frag_size" is an "ushort" while
PAGE_SHIFT here is 16. The commit changed the get_order() to be a
multi-line macro where compilers insist to check all statements in the
macro even when __builtin_constant_p(rx_frag_size) will return false as
"rx_frag_size" is a module parameter.

In file included from ./arch/powerpc/include/asm/page_64.h:107,
                 from ./arch/powerpc/include/asm/page.h:242,
                 from ./arch/powerpc/include/asm/mmu.h:132,
                 from ./arch/powerpc/include/asm/lppaca.h:47,
                 from ./arch/powerpc/include/asm/paca.h:17,
                 from ./arch/powerpc/include/asm/current.h:13,
                 from ./include/linux/thread_info.h:21,
                 from ./arch/powerpc/include/asm/processor.h:39,
                 from ./include/linux/prefetch.h:15,
                 from drivers/net/ethernet/emulex/benet/be_main.c:14:
drivers/net/ethernet/emulex/benet/be_main.c: In function
'be_rx_cqs_create':
./include/asm-generic/getorder.h:54:9: warning: comparison is always
true due to limited range of data type [-Wtype-limits]
   (((n) < (1UL << PAGE_SHIFT)) ? 0 :  \
         ^
drivers/net/ethernet/emulex/benet/be_main.c:3138:33: note: in expansion
of macro 'get_order'
  adapter->big_page_size = (1 << get_order(rx_frag_size)) * PAGE_SIZE;
                                 ^~~~~~~~~

Fix it by moving almost all of this multi-line macro into a proper
function __get_order(), and leave get_order() as a single-line macro in
order to avoid compilation errors.

Fixes: d66acc39c7ce ("bitops: Optimise get_order()")
Signed-off-by: Qian Cai <cai@....pw>
---
 include/asm-generic/getorder.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/asm-generic/getorder.h b/include/asm-generic/getorder.h
index c64bea7a52be..c6a6d3cd7007 100644
--- a/include/asm-generic/getorder.h
+++ b/include/asm-generic/getorder.h
@@ -15,6 +15,16 @@ int __get_order(unsigned long size)
 {
 	int order;
 
+	if (__builtin_constant_p(size)) {
+		if (!size)
+			return BITS_PER_LONG - PAGE_SHIFT;
+
+		if (size < (1UL << PAGE_SHIFT))
+			return 0;
+
+		return ilog2((size) - 1) - PAGE_SHIFT + 1;
+	}
+
 	size--;
 	size >>= PAGE_SHIFT;
 #if BITS_PER_LONG == 32
@@ -49,11 +59,6 @@ int __get_order(unsigned long size)
  */
 #define get_order(n)						\
 (								\
-	__builtin_constant_p(n) ? (				\
-		((n) == 0UL) ? BITS_PER_LONG - PAGE_SHIFT :	\
-		(((n) < (1UL << PAGE_SHIFT)) ? 0 :		\
-		 ilog2((n) - 1) - PAGE_SHIFT + 1)		\
-	) :							\
 	__get_order(n)						\
 )
 
-- 
1.8.3.1