From: Vitaly Wool <vitaly.wool@konsulko.com>
To: Mike Galbraith <efault@gmx.de>
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>
Subject: Re: [patch] zswap: fix zswap_frontswap_load() vs zsmalloc::map/unmap() might_sleep() splat
Date: Sat, 19 Dec 2020 11:46:29 +0100 [thread overview]
Message-ID: <CAM4kBBJZDqZfk+w5Wv4Ye7JythQ-Sr5-==zxeq8M5WCnHpFtEA@mail.gmail.com> (raw)
In-Reply-To: <6946d6e798866276f0d635f219cdd4ad05156351.camel@gmx.de>
On Sat, 19 Dec 2020, 11:27 Mike Galbraith, <efault@gmx.de> wrote:
>
> 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_sleep() splat
> > >
> > > zsmalloc map/unmap methods use preemption disabling bit spinlocks. Take the
> > > mutex outside of pool map/unmap methods in zswap_frontswap_load() as is 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.
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.
Best regards,
Vitaly
next prev parent reply other threads:[~2020-12-19 10:47 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-19 10:04 [patch] zswap: fix zswap_frontswap_load() vs zsmalloc::map/unmap() might_sleep() splat Mike Galbraith
2020-12-19 10:12 ` Mike Galbraith
2020-12-19 10:20 ` Vitaly Wool
2020-12-19 10:27 ` Mike Galbraith
2020-12-19 10:46 ` Vitaly Wool [this message]
2020-12-19 10:59 ` Mike Galbraith
2020-12-19 11:03 ` Mike Galbraith
2020-12-20 0:22 ` [PATCH] zsmalloc: do not use bit_spin_lock Vitaly Wool
2020-12-20 1:18 ` Matthew Wilcox
2020-12-20 7:21 ` Vitaly Wool
2021-01-14 16:17 ` Sebastian Andrzej Siewior
2020-12-20 1:23 ` Mike Galbraith
2020-12-20 4:11 ` Mike Galbraith
2020-12-20 7:47 ` Mike Galbraith
2020-12-20 21:20 ` Song Bao Hua (Barry Song)
2020-12-20 22:10 ` Mike Galbraith
2020-12-20 1:56 ` Mike Galbraith
2020-12-21 17:24 ` Minchan Kim
2020-12-21 19:20 ` Vitaly Wool
2020-12-21 19:50 ` Shakeel Butt
2020-12-21 20:05 ` Song Bao Hua (Barry Song)
2020-12-21 21:02 ` Shakeel Butt
2020-12-21 21:25 ` Song Bao Hua (Barry Song)
2020-12-21 22:11 ` Vitaly Wool
2020-12-21 22:42 ` Song Bao Hua (Barry Song)
2020-12-21 23:35 ` Song Bao Hua (Barry Song)
2020-12-22 0:59 ` Vitaly Wool
2020-12-22 1:10 ` Song Bao Hua (Barry Song)
2020-12-22 1:42 ` Song Bao Hua (Barry Song)
[not found] ` <CAM4kBBK=5eBdCjWc5VJXcdr=Z4PV1=ZQ2n8fZmJ6ahJbpUyv2A@mail.gmail.com>
2020-12-22 2:07 ` Song Bao Hua (Barry Song)
2020-12-22 2:10 ` Song Bao Hua (Barry Song)
2020-12-22 9:44 ` Vitaly Wool
2020-12-22 21:06 ` Song Bao Hua (Barry Song)
2020-12-23 0:11 ` Vitaly Wool
2020-12-23 12:44 ` tiantao (H)
2020-12-23 18:25 ` Vitaly Wool
2021-01-14 16:18 ` Sebastian Andrzej Siewior
2021-01-14 16:29 ` Vitaly Wool
2021-01-14 16:56 ` Sebastian Andrzej Siewior
2021-01-14 17:15 ` Vitaly Wool
2021-01-14 17:18 ` Sebastian Andrzej Siewior
2020-12-21 22:46 ` Shakeel Butt
2020-12-21 23:02 ` Song Bao Hua (Barry Song)
2020-12-22 9:20 ` David Laight
2020-12-21 20:22 ` Minchan Kim
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