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SubjectRE: [PATCH 06/11] Drivers: hv: vmbus: Use a spin lock for synchronizing channel scheduling vs. channel removal
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From: Andrea Parri (Microsoft) <parri.andrea@gmail.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@microsoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.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@microsoft.com>

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