linux-kernel - RE: [PATCH 06/11] Drivers: hv: vmbus: Use a spin lock for synchronizing channel scheduling vs. channel removal

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Message-ID: <DM5PR2101MB104791F7982BCD5FACD413EBD7DE0@DM5PR2101MB1047.namprd21.prod.outlook.com>
Date:   Fri, 10 Apr 2020 19:28:44 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     KY 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" <linux-hyperv@...r.kernel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        Boqun Feng <boqun.feng@...il.com>,
        vkuznets <vkuznets@...hat.com>
Subject: RE: [PATCH 06/11] Drivers: hv: vmbus: Use a spin lock for
 synchronizing channel scheduling vs. channel removal

From: Andrea Parri (Microsoft) <parri.andrea@...il.com> Sent: Sunday, April 5, 2020 5:15 PM
> 
> Since vmbus_chan_sched() dereferences the ring buffer pointer, we have
> to make sure that the ring buffer data structures don't get freed while
> such dereferencing is happening.  Current code does this by sending an
> IPI to the CPU that is allowed to access that ring buffer from interrupt
> level, cf., vmbus_reset_channel_cb().  But with the new functionality
> to allow changing the CPU that a channel will interrupt, we can't be
> sure what CPU will be running the vmbus_chan_sched() function for a
> particular channel, so the current IPI mechanism is infeasible.
> 
> Instead synchronize vmbus_chan_sched() and vmbus_reset_channel_cb() by
> using the (newly introduced) per-channel spin lock "sched_lock".  Move
> the test for onchannel_callback being NULL before the "switch" control
> statement in vmbus_chan_sched(), in order to not access the ring buffer
> if the vmbus_reset_channel_cb() has been completed on the channel.
> 
> Suggested-by: Michael Kelley <mikelley@...rosoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>
> ---
>  drivers/hv/channel.c      | 24 +++++++-----------------
>  drivers/hv/channel_mgmt.c |  1 +
>  drivers/hv/vmbus_drv.c    | 30 +++++++++++++++++-------------
>  include/linux/hyperv.h    |  6 ++++++
>  4 files changed, 31 insertions(+), 30 deletions(-)
> 

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