From: Andrew Morton <akpm@linux-foundation.org>
To: Christopher Lameter <cl@linux.com>
Cc: "Steven J. Hill" <steven.hill@cavium.com>, linux-mm@kvack.org
Subject: Re: mm/vmstat.c: fix vmstat_update() preemption BUG
Date: Thu, 29 Mar 2018 10:50:34 -0700 [thread overview]
Message-ID: <20180329105034.5fcc40fd5509ae74877d001e@linux-foundation.org> (raw)
In-Reply-To: <alpine.DEB.2.20.1803291126230.27735@nuc-kabylake>
On Thu, 29 Mar 2018 11:32:44 -0500 (CDT) Christopher Lameter <cl@linux.com> wrote:
> Just saw
>
> commit c7f26ccfb2c31eb1bf810ba13d044fcf583232db
> Author: Steven J. Hill <steven.hill@cavium.com>
> Date: Wed Mar 28 16:01:09 2018 -0700
>
> mm/vmstat.c: fix vmstat_update() preemption BUG
>
> Attempting to hotplug CPUs with CONFIG_VM_EVENT_COUNTERS enabled can
> cause vmstat_update() to report a BUG due to preemption not being
> disabled around smp_processor_id().
>
>
>
> The fix is wrong.
>
> vmstat_update cannot be moved to a differentprocessor and thus
> preemption should be off.
>
> vmstat_update repeatedly accesses per cpu information.
>
> vmstat_update first checks if there are counter to be updated on the
> current cpu and then updates the counters. This cannot happen if the
> process can be moved to a different cpu.
>
> The patch "switches off" preemption after the check if there are changes
> to the local per cpu counter.
>
> Lets find out what changed in the callers of vmstat_update() that caused
> the BUG to be triggered.
Yup. Please see the discussion at
http://lkml.kernel.org/r/1520881552-25659-1-git-send-email-steven.hill@cavium.com
- I'm suspecting that it's a shortcoming in
check_preemption_disabled(). But check_preemption_disabled() does
indeed check to see if the CPU is pinned to a single CPU so that
explanation doesn't fly. Maybe it's a glitch in the MIPS port - the
fact that it's triggered by CPU hotplugging makes me wonder if some
state got messed up.
prev parent reply other threads:[~2018-03-29 17:50 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-29 16:32 Christopher Lameter
2018-03-29 17:50 ` Andrew Morton [this message]
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