It is better to use wrapped smp_cond_load_relaxed instead of open-coded busy waiting for bit_spinlock.
Signed-off-by: Gao Xiang <[email protected]> --- change log v2: - fix the incorrect expression !(VAL >> (bitnum & (BITS_PER_LONG-1))) - the test result is described in the following reply. Thanks, Gao Xiang include/linux/bit_spinlock.h | 23 ++++++++++------------- 1 file changed, 10 insertions(+), 13 deletions(-) diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h index bbc4730a6505..d5f922b5ffd9 100644 --- a/include/linux/bit_spinlock.h +++ b/include/linux/bit_spinlock.h @@ -15,22 +15,19 @@ */ static inline void bit_spin_lock(int bitnum, unsigned long *addr) { - /* - * Assuming the lock is uncontended, this never enters - * the body of the outer loop. If it is contended, then - * within the inner loop a non-atomic test is used to - * busywait with less bus contention for a good time to - * attempt to acquire the lock bit. - */ - preempt_disable(); #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) - while (unlikely(test_and_set_bit_lock(bitnum, addr))) { - preempt_enable(); - do { - cpu_relax(); - } while (test_bit(bitnum, addr)); + const unsigned int bitshift = bitnum & (BITS_PER_LONG - 1); + + while (1) { + smp_cond_load_relaxed(&addr[BIT_WORD(bitnum)], + !((VAL >> bitshift) & 1)); preempt_disable(); + if (!test_and_set_bit_lock(bitnum, addr)) + break; + preempt_enable(); } +#else + preempt_disable(); #endif __acquire(bitlock); } -- 2.17.1
