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From:   Vitaly Wool <vitaly.wool@konsulko.com>
Date:   Sun, 20 Dec 2020 08:21:37 +0100
Message-ID: <CAM4kBBJCONeSBUwnH0rb3-cAn5THDFapQ8p8xt6+-VaobS_cWg@mail.gmail.com>
Subject: Re: [PATCH] zsmalloc: do not use bit_spin_lock
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Mike Galbraith <efault@gmx.de>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Barry Song <song.bao.hua@hisilicon.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Minchan Kim <minchan@kernel.org>,
        NitinGupta <ngupta@vflare.org>
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On Sun, Dec 20, 2020 at 2:18 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Sun, Dec 20, 2020 at 02:22:28AM +0200, Vitaly Wool wrote:
> > zsmalloc takes bit spinlock in its _map() callback and releases it
> > only in unmap() which is unsafe and leads to zswap complaining
> > about scheduling in atomic context.
> >
> > To fix that and to improve RT properties of zsmalloc, remove that
> > bit spinlock completely and use a bit flag instead.
>
> Isn't this just "I open coded bit spinlock to make the lockdep
> warnings go away"?

Not really because bit spinlock leaves preemption disabled.