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SubjectRe: [PATCH v2 1/1] scsi: fc: check for rport presence in fc_block_scsi_eh
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On 09/26/2017 08:58 AM, Johannes Thumshirn wrote:
> Coverity-scan recently found a possible NULL pointer dereference in
> fc_block_scsi_eh() as starget_to_rport() either returns the rport for
> the startget or NULL.
>
> While it is rather unlikely to have fc_block_scsi_eh() called without
> an rport associated it's a good idea to catch potential misuses of the
> API gracefully.
>
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
> ---
>
> Changes since v1:
> - s/WARN_ON/WARN_ON_ONCE/ (Bart)
>
> ---
> drivers/scsi/scsi_transport_fc.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c
> index ba9d70f8a6a1..38abff7b5dbc 100644
> --- a/drivers/scsi/scsi_transport_fc.c
> +++ b/drivers/scsi/scsi_transport_fc.c
> @@ -3328,6 +3328,9 @@ int fc_block_scsi_eh(struct scsi_cmnd *cmnd)
> {
> struct fc_rport *rport = starget_to_rport(scsi_target(cmnd->device));
>
> + if (WARN_ON_ONCE(!rport))
> + return 0;

Good idea.

However, return 0 or FAST_IO_FAIL?
I mean the callchains to this function (and of fc_block_rport()) react
differently depending on the return value.
Returning 0 means that the rport left the blocked state, i.e. is usable
for traffic again.
If there is no rport at all, I suppose one cannot use it for traffic.
If there is any I/O pending on this scope and we return 0, scsi_eh
escalates; and if this happens for a host_reset we end up with offlined
scsi_devices.
I wonder if returning FAST_IO_FAIL would be more appropriate here in
this case, in order to have scsi_eh let the pending I/O bubble up for a
timely path failover?

--
Mit freundlichen Grüßen / Kind regards
Steffen Maier

Linux on z Systems Development

IBM Deutschland Research & Development GmbH
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Geschaeftsfuehrung: Dirk Wittkopp
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