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authorAlexander Chumachenko <ledest@gmail.com>2010-04-01 15:34:52 +0300
committerH. Peter Anvin <hpa@zytor.com>2010-09-26 22:43:07 -0700
commitc9e2fbd909c20b165b2b9ffb59f8b674cf0a55b0 (patch)
tree29b4f977e3a1fa4b0b85057c35652ee5fe58949e /arch
parent7329cf0201f48695862e334828a108aa7175e955 (diff)
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 <ledest@gmail.com> Signed-off-by: Michael Shigorin <mike@osdn.org.ua> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/include/asm/bitops.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 545776efeb16..bafd80defa43 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)