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

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Message-ID: <20140605141425.GB3588@twins.programming.kicks-ass.net>
Date:	Thu, 5 Jun 2014 16:14:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
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 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.

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.

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