Re: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when hvsock's callback is running

[David Miller]

From: Dexuan Cui <decui@xxxxxxxxxxxxx>
Date: Tue, 28 Jul 2015 05:35:30 -0700

> In the SMP guest case, when the per-channel callback hvsock_events() is
> running on virtual CPU A, if the guest tries to close the connection on
> virtual CPU B: we invoke vmbus_close() -> vmbus_close_internal(),
> then we can have trouble: on B, vmbus_close_internal() will send IPI
> reset_channel_cb() to A, trying to set channel->onchannel_callbackto NULL;
> on A, if the IPI handler happens between
> "if (channel->onchannel_callback != NULL)" and invoking
> channel->onchannel_callback, we'll invoke a function pointer of NULL.
> 
> This is why the patch is necessary.
> 
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>

Sorry, I do not accept that you must use conditional locking and/or
IRQ disabling.

Boil it down to what is necessary for the least common denominator,
and use that unconditionally.
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