Re: [RFC PATCH v3 00/19] scsi: scsi_error: Introduce new error handle mechanism

[Diangang Li <lidiangang@bytedance.com>]

On Fri, Mar 14, 2025 at 08:55:25AM -0700, Bart Van Assche wrote:
> On 3/14/25 2:01 AM, Hannes Reinecke wrote:
> > 3. The current EH framework is designed around 'struct scsi_cmnd'.
> > Which means that the command _initiating_ the error handling can
> > only be returned once the _entire_ error handling (with all
> > escalations) is finished. And more often than not, the application
> > is waiting on that command to be completed before the next I/O
> > is sent. And that really limits the effectiveness of any improved
> > error handler; the application ultimatively has to wait for a
> > host reset before it can contine.
> > 
> > But anyway.
> > We already have a mechanism for asynchronous command aborts;
> > have you checked if you can adapt if for LUN reset, too?
> > That would be the easiest solution, I guess ...
> 
> Hmm ... does this mean submitting a LUN reset while concurrently new
> SCSI commands can be submitted from another thread? I don't think that's
> safe.
> 
> Additionally, how could a LUN reset help if a SCSI abort doesn't help?
> If a SCSI abort doesn't help, it probably means that the host controller
> locked up, e.g. due to a firmware bug. How to recover from this without
> resetting the host controller?
>

Hi Bart,

Based on our statistic data, nearly 80% of scsi_error_handler cases recover
successfully after scsi_eh_target_reset. The current solution effectively
prevents all targets under the host from being blocked, which is particularly
beneficial for servers with large numbers of HDD data disks.
 
> Thanks,
> 
> Bart.

Thanks,

Diangang Li