linux-kernel - Re: BUG_ON in rcu_sync

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Message-ID: <20160913152042.GA30160@redhat.com>
Date:   Tue, 13 Sep 2016 17:20:42 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Nikolay Borisov <kernel@...p.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: BUG_ON in rcu_sync_func triggered

On 09/13, Nikolay Borisov wrote:
>
> On 09/13/2016 05:35 PM, Nikolay Borisov wrote:
> >
> > On 09/13/2016 04:43 PM, Oleg Nesterov wrote:
> >> On 09/13, Oleg Nesterov wrote:
> >>>
> >>> OK... perhaps the unbalanced up_write... I'll try to look at freeze/thaw code,
> >>
> >> Heh, yes, it looks racy or I am totally confused.
> >>
> >>> could test the debugging patch below meanwhile?
> >>
> >> Yes please. I'll send you another patch (hopefully fix) later, but it
> >> would be nice if you can test this patch to get more info.
> >
> > I've already started testing with this patch on 4.4.20 this time

I think it would be better to stay with the same kernel version to
debug the problem...

> Actually forget that, here is a warning that this triggered:
>
> [  844.290454] WARNING: CPU: 2 PID: 1900 at kernel/rcu/sync.c:160 rcu_sync_func+0xc8/0x150()
> ...
> [  844.754708] XXX: ffff88047527da78 gp=2 cnt=0 cb=1

Hmm. Thanks. Please show us all the warnings you get.

Oleg.