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In order to use preempt_count() to track the interrupt disable nesting
level, __preempt_count_{add,sub}_return() are introduced, as their names
suggest, these primitives return the new value of the preempt_count()
after changing it. The following example shows the usage of it in
local_interrupt_disable():
// increase the HARDIRQ_DISABLE bit
new_count = __preempt_count_add_return(HARDIRQ_DISABLE_OFFSET);
// if it's the first-time increment, then disable the interrupt
// at hardware level.
if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET) {
local_irq_save(flags);
raw_cpu_write(local_interrupt_disable_state, flags);
}
Having these primitives will avoid a read of preempt_count() after
changing preempt_count() on certain architectures.
Signed-off-by: Boqun Feng <boqun@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com> # s390
Link: https://patch.msgid.link/20260804161447.84806-4-boqun@kernel.org
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