linux-kernel - Re: [RFC PATCH 02/11] Drivers: hv: vmbus: Don't bind the offer&rescind works to a specific CPU

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Message-ID: <20200328170833.GA10153@andrea>
Date:   Sat, 28 Mar 2020 18:08:33 +0100
From:   Andrea Parri <parri.andrea@...il.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Dexuan Cui <decui@...rosoft.com>,
        "K . Y . Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, linux-hyperv@...r.kernel.org,
        Michael Kelley <mikelley@...rosoft.com>,
        Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 02/11] Drivers: hv: vmbus: Don't bind the
 offer&rescind works to a specific CPU

> In case we believe that OFFER -> RESCINF sequence is always ordered
> by the host AND we don't care about other offers in the queue the
> suggested locking is OK: we're guaranteed to process RESCIND after we
> finished processing OFFER for the same channel. However, waiting for
> 'offer_in_progress == 0' looks fishy so I'd suggest we at least add a
> comment explaining that the wait is only needed to serialize us with
> possible OFFER for the same channel - and nothing else. I'd personally
> still slightly prefer the algorythm I suggested as it guarantees we take
> channel_mutex with offer_in_progress == 0 -- even if there are no issues
> we can think of today (not strongly though).

Does it?  offer_in_progress is incremented without channel_mutex...

IAC, I have no objections to apply the changes you suggested.  To avoid
misunderstandings: vmbus_bus_suspend() presents a similar usage...  Are
you suggesting that I apply similar changes there?

Alternatively:  FWIW, the comment in vmbus_onoffer_rescind() does refer
to "The offer msg and the corresponding rescind msg...".  I am all ears
if you have any concrete suggestions to improve these comments.

Thanks,
  Andrea