From 70e6a20b3720e522633f4b791f2f35e817d7ced3 Mon Sep 17 00:00:00 2001 From: Led Date: Thu, 1 Apr 2010 15:34:52 +0300 Subject: [PATCH] x86: avoid 'constant_test_bit()' misoptimization due to cast to non-volatile While debugging bit_spin_lock() hang, it was tracked down to gcc-4.4 misoptimization of non-inlined constant_test_bit() due to non-volatile addr when 'const volatile unsigned long *addr' cast to 'unsigned long *' with subsequent unconditional jump to pause (and not to the test) leading to hang. Compiling with gcc-4.3 or disabling CONFIG_OPTIMIZE_INLINING yields inlined constant_test_bit() and correct jump, thus working around the kernel bug. Other arches than asm-x86 may implement this slightly differently; 2.6.29 mitigates the misoptimization by changing the function prototype (commit c4295fbb6048d85f0b41c5ced5cbf63f6811c46c) but probably fixing the issue itself is better. Signed-off-by: Alexander Chumachenko Signed-off-by: Michael Shigorin --- arch/x86/include/asm/bitops.h | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h index 545776e..bafd80d 100644 --- a/arch/x86/include/asm/bitops.h +++ b/arch/x86/include/asm/bitops.h @@ -309,7 +309,7 @@ static inline int test_and_change_bit(int nr, volatile unsigned long *addr) static __always_inline int constant_test_bit(unsigned int nr, const volatile unsigned long *addr) { return ((1UL << (nr % BITS_PER_LONG)) & - (((unsigned long *)addr)[nr / BITS_PER_LONG])) != 0; + (addr[nr / BITS_PER_LONG])) != 0; } static inline int variable_test_bit(int nr, volatile const unsigned long *addr) -- 1.7.2.3