linux-kernel - Re: [patch] zswap: fix zswap_frontswap_load() vs zsmalloc::map/unmap() might

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <18669bd607ae9efbf4e00e36532c7aa167d0fa12.camel@gmx.de>
Date:   Sat, 19 Dec 2020 11:59:33 +0100
From:   Mike Galbraith <efault@....de>
To:     Vitaly Wool <vitaly.wool@...sulko.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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, <efault@....de> wrote:
>
> > 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.

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

	-Mike