linux-kernel - Re: [next-20180517][ppc] watchdog: CPU 88 self-detected hard LOCKUP @ update_cfs

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Date:   Tue, 29 May 2018 18:39:40 +0530
From:   Abdul Haleem <abdhalee@...ux.vnet.ibm.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     sachinp <sachinp@...ux.vnet.ibm.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-next <linux-next@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [next-20180517][ppc] watchdog: CPU 88 self-detected hard LOCKUP
 @ update_cfs_group+0x30/0x150

On Mon, 2018-05-21 at 16:50 +1000, Nicholas Piggin wrote:
> Ah, it's POWER8.
> 
> I'm betting we have a bug with nohz timer offloading somewhere.
> 
> I *think* we may have seen similar on P9 as well, but that may be
> related to problems with stop states.
> 
> Can you reproduce it easily? I'm thinking maybe adding some
> tracepoints that track decrementer settings and interrupts, and
> nohz offload activity might show something up.

Yes, the problem is reproducible consistently on our CI setup and today
It triggered on 4.17.0-rc6 (mainline) too.

-- 
Regard's

Abdul Haleem
IBM Linux Technology Centre