PREEMP_ACTIVE in cond_resched

["Dong Feng" <middle.fengdong@gmail.com>]

cond_resched() checks and conditionally sets PREEMPT_ACTIVE flag for
the current task. The comments says,

/*
* The BKS might be reacquired before we have dropped
* PREEMPT_ACTIVE, which could trigger a second
* cond_resched() call.
*/

My understanding is that cond_resched() would be indirectly invoked
twice recursively, through the following path,

cond_resched() -> schedule() -> reacquire_kernel_lock() -> down() ->
might_sleep() -> might_resched() -> cond_resched().

However, the above path is possible only in a voluntary-preemptive
kernel. In a full-preemptive kernel, I do not find any possible path
to cause recursive cond_resched(). Does that mean we can actually
remove the check and setting of PREEMPT_ACTIVE for a full-preemptive
kernel?
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