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From:   Michael Kelley <mikelley@microsoft.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        vkuznets <vkuznets@redhat.com>
Subject: RE: [PATCH 05/11] hv_utils: Always execute the fcopy and vss
 callbacks in a tasklet
Thread-Topic: [PATCH 05/11] hv_utils: Always execute the fcopy and vss
 callbacks in a tasklet
Thread-Index: AQHWC6irB8fFAbLJ/0KQru+QGYYm6qhywuPA
Date:   Fri, 10 Apr 2020 19:26:56 +0000
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 <20200406001514.19876-6-parri.andrea@gmail.com>
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From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Sunday, April=
 5, 2020 5:15 PM
>=20
> The fcopy and vss callback functions could be running in a tasklet
> at the same time they are called in hv_poll_channel().  Current code
> serializes the invocations of these functions, and their accesses to
> the channel ring buffer, by sending an IPI to the CPU that is allowed
> to access the ring buffer, cf. hv_poll_channel().  This IPI mechanism
> becomes infeasible if we allow changing the CPU that a channel will
> interrupt.  Instead modify the callback wrappers to always execute
> the fcopy and vss callbacks in a tasklet, thus mirroring the solution
> for the kvp callback functions adopted since commit a3ade8cc474d8
> ("HV: properly delay KVP packets when negotiation is in progress").
> This will ensure that the callback function can't run on two CPUs at
> the same time.
>=20
> Suggested-by: Michael Kelley <mikelley@microsoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> ---
>  drivers/hv/hv_fcopy.c     | 2 +-
>  drivers/hv/hv_snapshot.c  | 2 +-
>  drivers/hv/hyperv_vmbus.h | 7 +------
>  3 files changed, 3 insertions(+), 8 deletions(-)
>=20

Reviewed-by: Michael Kelley <mikelley@microsoft.com>