Re: [PATCHv2 0/5] SCSI EH cleanup

[Bart Van Assche <Bart.VanAssche@sandisk.com>]

On Wed, 2017-02-22 at 17:07 +0100, Hannes Reinecke wrote:
> Primary goal is to make asynchronous aborts mandatory; there hasn't
> been a single report so far where asynchronous abort won't work, so
> the 'no_async_abort' flag has never been used and will be removed
> with this patchset.

Hello Hannes,

There is a problem with asynchronous aborts. Some SCSI drivers, e.g. ib_srp,
support fast error recovery by performing a transport layer reconnect without
reporting this event as a failure to the SCSI core. While such a reconnect is
ongoing it is important that no attempt is made to use the data structures
that represent the connection. Hence the scsi_target_block() call in
srp_reconnect_rport(). This blocks most .queuecommand() calls except those
that originate from the SCSI EH. Hence the if (current == shost->ehandler)
mutex_lock(&rport->mutex) code in srp_queuecommand(). Asynchronous aborts
break this code because the asynchronous abort code submits an abort from
another context than the SCSI EH thread. I know that this way of detecting
the SCSI EH context is not an optimal solution. A few years ago I have tried
to modify the SCSI EH such that reconnects and .queuecommand() calls could
be serialized but James was not interested in such patches at that time.

Bart.