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Re: 2.6 preemptive kernel on mips

To: jsun@junsun.net
Subject: Re: 2.6 preemptive kernel on mips
From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Date: Tue, 05 Oct 2004 13:58:45 +0900 (JST)
Cc: jsun@mvista.com, wsonguci@yahoo.com, linux-mips@linux-mips.org
In-reply-to: <20041005000002.GB9718@gateway.junsun.net>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20040803124048.C1926@mvista.com> <20041004.211504.03974923.nemoto@toshiba-tops.co.jp> <20041005000002.GB9718@gateway.junsun.net>
Sender: linux-mips-bounce@linux-mips.org
>>>>> On Mon, 4 Oct 2004 17:00:02 -0700, Jun Sun <jsun@junsun.net> said:
>> It lacks some preempt_disable/preempt_enable which were in
>> preempt-patch for 2.4 kernel.  Are these all unnecessary at all?

jsun> They are necessary.

>> For example, fpu-emulation is not preemptive-safe, isn't it?

jsun> That is correct.

jsun> I think the best thing to do right now is to go through 2.4
jsun> preemption patch and pick up the missing ones for 2.6.

Thank you.  I think there are some issue to fix.

1. ll/sc emulation (ll_bit, ll_task).  This is easy to fix.

2. There is an global variable ieee754_csr in math-emu.  This must be
protected by preempt_disable.  But math-emu uses put_user/get_user
which can not be used with preempt disabled.  (Is it true?)

3. save_fp_context/restore_fp_context is not preemptable.  But these
function uses put_user/get_user.


Actually, math-emu/fp_context issues are not only for preemptive
kernel.  I suppose bad things can happen if a process going to sleep
on get_user/put_user in math-emu/save_fp_context/restore_fp_context...

---
Atsushi Nemoto

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