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There are cpumask_test_and_clear_cpu/cpumask_setall() APIs, it seems > > > that API cpumask_setall() does not support atomic operation. > > > > > > Do you think it is reasonable to add new API similar with cpumask_setall() > > > which supports atomic operation? > > > > Maybe reasonable, but it's impossible. cpumask is a bitmap, which in > > turn is an array of unsigned longs. There's no atomic operations on > > arrays. > It should be workable with atomic operation on unsigned long, rather than > the array of unsigned longs, the API cpumask_test_and_clear_cpu is atomic > operation on unsigned long also. No, cpumask_test_and_clear_cpu is atomic() operates on cpumask_t*, which is a pointer to unsigned long. > Is it ok to use smp_store_mb() to fill the bitmap with the similar API > cpumask_setall()? where xchg() is used in smp_store_mb() wrapper instead. If your bitmap is longer than 1 word, you'll have to issue 2 or more smp_store_mb()'s. Then, a series of atomic operations is not atomic itself.