Re: [PATCH] BUG(): sched.c: Line 944

From: Ingo Molnar (
Date: Tue Sep 17 2002 - 13:46:29 EST

On 17 Sep 2002, Robert Love wrote:

> [...] How can this in_atomic() test _ever_ catch a preemption bug? We
> cannot enter the scheduler off kernel preemption unless
> preempt_count==0. This is a test to catch bugs in other parts of the
> kernel, e.g. where code explicitly calls schedule() while holding a
> lock.

you are right, i was confusing this with the older check for disabled
interrupt in preempt_schedule() [which i'd still find useful].

The smp_processor_id() test catches true preemption bugs. So does
preempt_count() underflow detection.

i do agree with Alan - there can be nothing bad in trying to fix all that
non-preempt-aware code right now, before it becomes too late.


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