From: Eric Farman <farman@linux.ibm.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: Cornelia Huck <cohuck@redhat.com>,
Matthew Rosato <mjrosato@linux.ibm.com>,
Jared Rossi <jrossi@linux.ibm.com>,
linux-s390@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [RFC PATCH v4 0/4] vfio-ccw: Fix interrupt handling for HALT/CLEAR
Date: Fri, 23 Apr 2021 15:07:17 -0400 [thread overview]
Message-ID: <986a165f08d29110e86c044359111582332a4ccb.camel@linux.ibm.com> (raw)
In-Reply-To: <20210423190853.6b159871.pasic@linux.ibm.com>
On Fri, 2021-04-23 at 19:08 +0200, Halil Pasic wrote:
> On Fri, 23 Apr 2021 11:53:06 -0400
> Eric Farman <farman@linux.ibm.com> wrote:
>
> > > Is in your opinion the vfio-ccw kernel module data race free with
> > > this
> > > series applied?
> >
> > I have no further concerns.
>
> I take this for a "yes, in my opinion it is data race free".
You asked about once this series is applied, which it is not.
>
> Please explain me, how do we synchronize access to
> a) private->state
> b) cp->initialized?
>
> Asuming we both use the definition from the C standard, the multiple
> threads potentially concurrently accessing private->state or
> cp->initialized are not hard to find.
>
Correct. The examples you provide below are the subject of patch 2,
which has already been identified as having issues and will be
reworked.
Thanks,
Eric
> For the former you can take vfio_ccw_sch_io_todo() (has both a read
> and a write, and runs from the workqueue) and fsm_io_request() (has
> both read and write). I guess the accesses from fsm_io_request() are
> all with the io_mutex held, but the accesses form
> vfio_ccw_sch_io_todo()
> are not with the io_mutex held AFAICT.
>
> And the same is true for the latter with the difference that
> vfio_ccw_sch_io_todo() manipulates cp->initialized via
> cp_update_scsw()
> and cp_free().
>
> These are either data races, or I'm missing something. Let me also
> note that C programs data races are bad news, because of undefined
> behavior.
>
> Regards,
> Halil
>
>
next prev parent reply other threads:[~2021-04-23 19:07 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 18:24 [RFC PATCH v4 0/4] vfio-ccw: Fix interrupt handling for HALT/CLEAR Eric Farman
2021-04-13 18:24 ` [RFC PATCH v4 1/4] vfio-ccw: Check initialized flag in cp_init() Eric Farman
2021-04-14 16:30 ` Cornelia Huck
2021-04-13 18:24 ` [RFC PATCH v4 2/4] vfio-ccw: Check workqueue before doing START Eric Farman
2021-04-15 10:51 ` Cornelia Huck
2021-04-15 13:48 ` Eric Farman
2021-04-15 16:19 ` Cornelia Huck
2021-04-15 18:42 ` Eric Farman
2021-04-16 14:41 ` Cornelia Huck
2021-04-13 18:24 ` [RFC PATCH v4 3/4] vfio-ccw: Reset FSM state to IDLE inside FSM Eric Farman
2021-04-15 10:54 ` Cornelia Huck
2021-04-13 18:24 ` [RFC PATCH v4 4/4] vfio-ccw: Reset FSM state to IDLE before io_mutex Eric Farman
2021-04-21 10:25 ` Cornelia Huck
2021-04-21 12:58 ` Eric Farman
2021-04-22 16:16 ` Eric Farman
2021-04-22 0:52 ` [RFC PATCH v4 0/4] vfio-ccw: Fix interrupt handling for HALT/CLEAR Halil Pasic
2021-04-22 20:49 ` Eric Farman
2021-04-23 11:06 ` Cornelia Huck
2021-04-23 13:23 ` Halil Pasic
2021-04-23 13:28 ` Niklas Schnelle
2021-04-23 15:53 ` Eric Farman
2021-04-23 11:50 ` Halil Pasic
2021-04-23 15:53 ` Eric Farman
2021-04-23 17:08 ` Halil Pasic
2021-04-23 19:07 ` Eric Farman [this message]
2021-04-24 0:18 ` Halil Pasic
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