linux-kernel - Re: Sleeping BUG in khugepaged for i586

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Message-ID: <d348054d-3857-65bb-e896-c4bd2ea6ee85@suse.cz>
Date:   Fri, 9 Jun 2017 08:48:58 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>,
        Matthew Wilcox <willy@...radead.org>
Cc:     David Rientjes <rientjes@...gle.com>,
        Larry Finger <Larry.Finger@...inger.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: Sleeping BUG in khugepaged for i586

On 06/08/2017 10:30 PM, Michal Hocko wrote:
> But I guess you are primary after syncing the preemptive mode for 64 and
> 32b systems, right? I agree that having a different model is more than
> unfortunate because 32b gets much less testing coverage and so a risk of
> introducing a new bug is just a matter of time. Maybe we should make
> pte_offset_map disable preemption and currently noop pte_unmap to
> preempt_enable. The overhead should be pretty marginal on x86_64 but not
> all arches have per-cpu preempt count. So I am not sure we really want
> to add this to just for the debugging purposes...

I think adding that overhead for everyone would be unfortunate. It would
be acceptable, if it was done only for the config option that enables
the might_sleep() checks (CONFIG_DEBUG_ATOMIC_SLEEP?)

Vlastimil