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From: kumon@flab.fujitsu.co.jp
Date: Thu, 2 Nov 2000 21:50:08 +0900
Message-Id: <200011021250.VAA24349@asami.proc.flab.fujitsu.co.jp>
To: kumon@flab.fujitsu.co.jp
Cc: Andrew Morton <andrewm@uow.edu.au>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Re: Negative scalability by removal of lock_kernel()?(Was: 
 Strange performance behavior of 2.4.0-test9)
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kumon@flab.fujitsu.co.jp writes:
 > Your last patch makes the problem very clear.
 > 
 > 2.4.0-test10-pre5 with the LIFO patch (P3), we can't get the values.

It dies at the following line in kernel/sched.c:schedule() 

move_rr_back:

	switch (prev->state & ~TASK_EXCLUSIVE) {
		case TASK_INTERRUPTIBLE:
			if (signal_pending(prev)) {
				prev->state = TASK_RUNNING;
				break;
			}
		default:
here==>			del_from_runqueue(prev);
		case TASK_RUNNING:
	}


"prev" contains a run_list structure and prev->run_list.next pointed
to NULL.  This caused the bus-error in __list_del().

# actually the CPU accesses address 0x4 (4 is offset to prev within
# run_list).

BTW, why this switch statement has less breaks at everywhere.

--
Computer Systems Laboratory, Fujitsu Labs.
kumon@flab.fujitsu.co.jp
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