diff options
| author | Alexander Chumachenko <ledest@gmail.com> | 2010-04-01 15:34:52 +0300 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2010-09-26 22:43:07 -0700 |
| commit | c9e2fbd909c20b165b2b9ffb59f8b674cf0a55b0 (patch) | |
| tree | 29b4f977e3a1fa4b0b85057c35652ee5fe58949e | |
| parent | 7329cf0201f48695862e334828a108aa7175e955 (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>
| -rw-r--r-- | 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 545776efeb1..bafd80defa4 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) |