fe8712f84a
Fix the race between ioat_reset_hw and ioat_process_events. HW reset isn't protected by a lock because it can sleep for a long time (40.1 ms). This resulted in a race where we would process bogus parts of the descriptor ring as if it had completed. This looked like duplicate completions on old events, if your ring had looped at least once. Block callout and interrupt work while reset runs so the completion end of things does not observe indeterminate state and process invalid parts of the ring. Start the channel with a manually implemented ioat_null() to keep other submitters quiesced while we wait for the channel to start (100 us). r295605 may have made the race between ioat_reset_hw and ioat_process_events wider, but I believe it already existed before that revision. ioat_process_events can be invoked by two asynchronous sources: callout (softclock) and device interrupt. Those could race each other, to the same effect. Reviewed by: markj Approved by: re Sponsored by: EMC / Isilon Storage Division Differential Revision: https://reviews.freebsd.org/D7097
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