Messages in this thread | | | Date | Mon, 24 Aug 2015 10:43:28 -0700 (PDT) | Subject | Re: [PATCH] usbnet: Fix two races between usbnet_stop() and the BH | From | David Miller <> |
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From: Eugene Shatokhin <eugene.shatokhin@rosalab.ru> Date: Wed, 19 Aug 2015 14:59:01 +0300
> So the following might be possible, although unlikely: > > CPU0 CPU1 > clear_bit: read dev->flags > clear_bit: clear EVENT_RX_KILL in the read value > > dev->flags=0; > > clear_bit: write updated dev->flags > > As a result, dev->flags may become non-zero again.
Is this really possible?
Stores really are "atomic" in the sense that the do their update in one indivisible operation.
Atomic operations like clear_bit also will behave that way.
If a clear_bit is in progress, the "dev->flags=0" store will not be able to grab the cache line exclusively until the clear_bit is done.
So I think the above sequent of events is completely impossible. Once a clear_bit starts, a write by another foreign agent on the bus is absolutely impossible to legally occur until the clear_bit completes.
I think this is a non-issue.
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