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Date:   Thu, 8 Jul 2021 06:17:37 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Michael Schmitz <schmitzmic@gmail.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Christoph Hellwig <hch@lst.de>,
        Greg Ungerer <gerg@linux-m68k.org>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>,
        uClinux development list <uclinux-dev@uclinux.org>
Subject: Re: [PATCH] m68knommu: remove set_fs()
Message-ID: <20210708041737.GB17410@lst.de>
References: <20210705055719.949875-1-hch@lst.de> <20210705055719.949875-2-hch@lst.de> <CAMuHMdV4UQaKE7fn0_HhPfHzwEMwouPvqoeW6_V13yebe7ZSQQ@mail.gmail.com> <CAHk-=wgjWebav7K_F7WS7KiwOAYr8KktsZiaV+jYP5LU5RB3Sg@mail.gmail.com> <3c736dc7-dd0c-0691-ece4-e7dc9aaa3a54@gmail.com> <CAHk-=wjPcjY0TUNeh1pwC2s4xk=MPJGu_66+ywJ3SbmrEW5Yxg@mail.gmail.com>
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On Wed, Jul 07, 2021 at 09:14:29PM -0700, Linus Torvalds wrote:
> Except now that I think about it, I worry about getting scheduled away
> *between* the instruction that sets SFC and the one that sets DFC. And
> then switch_to() will save just SFC to the thread-struct. And then
> restore the (new thread) SFC value to _both_ SFC and DFC.

arch/m68k/Kconfig:      select ARCH_NO_PREEMPT if !COLDFIRE

So only coldfire can support kernel preemption, and coldfire never uses
SFC/DFC.