ATA driver races with interrupts
will+freebsd-current at will.iki.fi
Tue Aug 3 02:28:01 PDT 2004
Søren Schmidt wrote:
> We dont want to disable interrupts, ever.
That makes avoiding races difficult for some hardware...
> I have one change in a tree here that you could try, but as long as
> the hardware doesn't support proper interrupt status its impossible to
> close the race window completely. Please remember that this is part of
> a bigger patchset, so I might have edited it too much, YMMV,,
It introduces the same race as my patch - if the interrupt occurs after
ATA_DMA_ACTIVE is set but before running is set, the interrupt may be
acknowledged (I assume that's what writing BMSTAT_PORT does) but ignored
(because running == NULL).
It seems to me that reliable solutions would all involve atomically
(from an interrupt perspective) performing the final activation of the
transaction and marking the transaction active for the interrupt handler
to check. What the correct way to ensure such atomicity in -current is,
I don't know.
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