On Tue, May 31, 2016 at 1:38 AM, Wei Fang [off-list ref] wrote:

sas_ata_strategy_handler() adds the works of the ata error handler
to system_unbound_wq. This workqueue asynchronously runs work items,
so the ata error handler will be performed concurrently on different
CPUs. In this case, ->host_failed will be decreased simultaneously in
scsi_eh_finish_cmd() on different CPUs, and become abnormal.

It will lead to permanently inequal between ->host_failed and
 ->host_busy, and scsi error handler thread won't become running.
IO errors after that won't be handled forever.

Use atomic type for ->host_failed to fix this race.

This fixes the problem introduced in
commit 50824d6c5657 ("[SCSI] libsas: async ata-eh").

Reviewed-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Wei Fang <redacted>

Acked-by: Dan Williams <redacted>