Re: [PATCH v3 1/2] scsi: fix race between simultaneous decrements of ->host_failed

[James Bottomley <jejb@linux.vnet.ibm.com>]

On Thu, 2016-06-02 at 16:42 +0800, Wei Fang 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.
> 
> Since all scmds must have been handled in the strategy handle, just
> remove the decrement in scsi_eh_finish_cmd() and zero ->host_busy
> after the strategy handle to fix this race.
> 
> This fixes the problem introduced in
> commit 50824d6c5657 ("[SCSI] libsas: async ata-eh").
> 
> Signed-off-by: Wei Fang <fangwei1@huawei.com>
> ---
> Changes v1->v2:
> - update Documentation/scsi/scsi_eh.txt about ->host_failed
> Changes v2->v3:
> - don't use atomic type, just zero ->host_failed after the strategy
> handle

Reviewed-by: James Bottomley <jejb@linux.vnet.ibm.com>