linux-kernel - Re: [PATCH 5/9] perf/x86: implement cross-HT corruption bug workaround

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Message-ID: <CAHzUATgi3eRKs4V4KEsQTiiUAE_vLYOebGT501CRp9F9eim21w@mail.gmail.com>
Date:	Thu, 5 Jun 2014 17:24:30 +0300
From:	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, ak@...ux.intel.com,
	jolsa@...hat.com, zheng.z.yan@...el.com
Subject: Re: [PATCH 5/9] perf/x86: implement cross-HT corruption bug workaround

On Thu, Jun 5, 2014 at 5:14 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Jun 05, 2014 at 04:11:50PM +0200, Peter Zijlstra wrote:
>> > > x86_schedule_event()
>> > >   ->start_scheduling()
>> > >     spin_lock()
>> > >   ->get_event_constraints()
>> > >     intel_get_excl_constraints()
>> > >       kmalloc(.gfp=GFP_KERNEL)
>> > >
>> > > How can that ever work?
>>
>> > Are you saying it is illegal to call kmalloc() from
>> > this context?
>>
>> Nobody will come and arrest you for it, so no. Broken though. GFP_KERNEL
>> will attempt to sleep to wait for reclaim, and you're holding a
>> spinlock.

Ok, got it.

>
> Furthermore, even GFP_ATOMIC shouldn't be used because these are/should
> be raw_spinlocks and the zone->lock is a regular spinlock.
>
> So please look into the preallocation thing.

We will preallocate.
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