linux-kernel - PREEMP_ACTIVE in cond

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Message-ID: <a2ebde260702211900v29c3f9a3y45ec5867e36b7a4b@mail.gmail.com>
Date:	Thu, 22 Feb 2007 11:00:16 +0800
From:	"Dong Feng" <middle.fengdong@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: PREEMP_ACTIVE in cond_resched

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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