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Subject: Re: Patch: linux-2.5.8-pre1/kernel/exit.c change caused BUG() at
	boot time
From: Robert Love <rml@tech9.net>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Dave Hansen <haveblue@us.ibm.com>, "Adam J. Richter" <adam@yggdrasil.com>,
        linux-kernel@vger.kernel.org
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Date: 04 Apr 2002 14:26:22 -0500
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On Thu, 2002-04-04 at 14:14, Linus Torvalds wrote:

> The answer is that preempt_schedule() illegally sets 
> 
> 	current->state = TASK_RUNNING;
> 
> without asking the process whether that's ok. The SMP code never does 
> anything like that.

Well Ingo added that ;)

We used to just set a flag in the preempt_count that marked the task as
preempted and made sure on its next trip into schedule it ran again.

Do you think it is better to deny preemption if state==TASK_ZOMBIE (note
this requires code in preempt_schedule and the interrupt return path,
since Ingo decoupled the two) or just disable preemption around critical
regions caused by setting state to TASK_ZOMBIE ?

I suspect this is the first occurrence of a problem of this kind ... and
the attached patch handles it.

	Robert Love

diff -urN linux-2.5.8-pre1/kernel/exit.c linux/kernel/exit.c
--- linux-2.5.8-pre1/kernel/exit.c	Wed Apr  3 20:57:37 2002
+++ linux/kernel/exit.c	Thu Apr  4 14:22:30 2002
@@ -499,6 +499,8 @@
 	acct_process(code);
 	__exit_mm(tsk);
 
+	preempt_disable();
+
 	sem_exit();
 	__exit_files(tsk);
 	__exit_fs(tsk);
@@ -515,6 +517,7 @@
 
 	tsk->exit_code = code;
 	exit_notify();
+	preempt_enable_no_resched();
 	schedule();
 	BUG();
 /*


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