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Date:   Sat, 19 Dec 2020 11:59:33 +0100
From:   Mike Galbraith <>
To:     Vitaly Wool <>
Cc:     LKML <>, linux-mm <>,
        Barry Song <>,
        Sebastian Andrzej Siewior <>
Subject: Re: [patch] zswap: fix zswap_frontswap_load() vs
 zsmalloc::map/unmap() might_sleep() splat

On Sat, 2020-12-19 at 11:46 +0100, Vitaly Wool wrote:
> On Sat, 19 Dec 2020, 11:27 Mike Galbraith, <> wrote:
> > The kernel that generated that splat was NOT an RT kernel, it was plain
> > with a PREEMPT config.
> I see, thanks. I don't think it makes things better for zsmalloc
> though. From what I can see, the offending code is this:
> >        /* From now on, migration cannot move the object */
> >        pin_tag(handle);
> Bit spinlock is taken in pin_tag(). I find the comment above somewhat
> misleading, why is it necessary to take a spinlock to prevent
> migration? I would guess an atomic flag should normally be enough.
> zswap is not broken here, it is zsmalloc that needs to be fixed.

Cool, those damn bit spinlocks going away would be a case of happiness
for RT as well :)


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