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Message-ID: <6946d6e798866276f0d635f219cdd4ad05156351.camel@gmx.de>
Subject: Re: [patch] zswap: fix zswap_frontswap_load() vs
 zsmalloc::map/unmap() might_sleep() splat
From:   Mike Galbraith <efault@gmx.de>
To:     Vitaly Wool <vitaly.wool@konsulko.com>
Cc:     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>
Date:   Sat, 19 Dec 2020 11:27:00 +0100
In-Reply-To: <CAM4kBBJYZzbXAixrKvy9MeO2eUsVVi8=iUBUc+pbSMXudy7hkw@mail.gmail.com>
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On Sat, 2020-12-19 at 11:20 +0100, Vitaly Wool wrote:
> Hi Mike,
>
> On Sat, Dec 19, 2020 at 11:12 AM Mike Galbraith <efault@gmx.de> wrote:
> >
> > (mailer partially munged formatting? resend)
> >
> > mm/zswap: fix zswap_frontswap_load() vs zsmalloc::map/unmap() might_sl=
eep() splat
> >
> > zsmalloc map/unmap methods use preemption disabling bit spinlocks.  Ta=
ke the
> > mutex outside of pool map/unmap methods in zswap_frontswap_load() as i=
s done
> > in zswap_frontswap_store().
>
> oh wait... So is zsmalloc taking a spin lock in its map callback and
> releasing it only in unmap? In this case, I would rather keep zswap as
> is, mark zsmalloc as RT unsafe and have zsmalloc maintainer fix it.

The kernel that generated that splat was NOT an RT kernel, it was plain
master.today with a PREEMPT config.

	-Mike