linux-kernel - Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard policy

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Message-ID: <20160219150933.GB25910@potion.brq.redhat.com>
Date:	Fri, 19 Feb 2016 16:09:34 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Yuki Shibuya <shibuya.yk@...s.nec.co.jp>
Subject: Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard
 policy

2016-02-19 16:06+0100, Paolo Bonzini:
> On 19/02/2016 16:04, Radim Krčmář wrote:
>>>> ... so in patch 7 concurrent _writes_ of reinject are protected by the
>>>> lock, but reads are done outside it (in pit_timer_fn).  WDYT about
>>>> making reinject an atomic_t?
>> There was/is no harm in having reinject non-atomic.  This patch added
>> notifiers, which is the reason for re-introducing a mutex.
>> 
>> Userspace can (and SHOULDN'T) call this function multiple times,
>> concurrently, so the mutex prevents a situations where, e.g. only one
>> notifier is registered in the end.
> 
> Yes, I understand why you added the mutex here; good catch indeed.  The
> atomic_t is just to show that it's okay to read it outside the lock.
> It's just for a bit of extra documentation.

Hm, good point.  I will add it.  Thanks.