On 1/19/24 3:02 AM, John Garry wrote: > On 18/01/2024 17:22, Brian King wrote: >> On 1/18/24 9:44 AM, John Garry wrote: >>> On 17/01/2024 21:36, Brian King wrote: >>>> This addresses an issue discovered on ibmvfc LUNs. For this driver, >>>> max_sectors is negotiated with the VIOS. This gets done at initialization >>>> time, then LUNs get scanned and things generally work fine. However, >>>> this attribute can be changed on the VIOS, either due to a sysadmin >>>> change or potentially a VIOS code level change. If this decreases >>>> to a smaller value, due to one of these reasons, the next time the >>>> ibmvfc driver performs an NPIV login, it will only be able to use >>>> the smaller value. In the case of a VIOS reboot, when the VIOS goes >>>> down, all paths through that VIOS will go to devloss state. When >>>> the VIOS comes back up, ibmvfc negotiates max_sectors and will only >>>> be able to get the smaller value and it will update shost->max_sectors. >>> >>> Are you saying that the driver will manually update shost->max_sectors after adding the scsi host? I didn't think that was permitted. >> >> That is what happens. The characteristics of the underlying hardware can change across >> a virtual adapter reset. > > That's unfortunate. > > I don't think that it's a good idea to change shost->max_sectors after adding the scsi host or to add core code to condone doing it. Indeed, there is code there to limit shost->max_sectors from DMA mapping constraints in scsi_add_host() path, which should not be ignored. Good point. However, this patch only lowers max_hw sectors if shost->max_sectors has since been decreased. > > Would it be possible to initially set shost->max_sectors for this adapter at the lowest anticipated value for that adapter and don't change thereafter? Different physical backing devices support different ranges of values and the physical backing device can change dynamically. There is currently no defined way for the client to determine what the lowest possible value is. The downside to adding such an attribute would be that we'd then always be limited to an arbitrarily small value, which would limit the performance. Thanks, Brian > > Thanks, > John > >> >> Thanks, >> >> Brian >> >>> >>> Thanks, >>> John >>> >>>> However, when LUNs are scanned, the devloss paths will be found >>>> and brought back online, still using the old max_hw_sectors. This >>>> change ensures that max_hw_sectors gets updated. >>>> >>>> Signed-off-by: Brian King <brking@xxxxxxxxxxxxxxxxxx> >>>> --- >>>> drivers/scsi/scsi_scan.c | 6 +++++- >>>> 1 file changed, 5 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c >>>> index 44680f65ea14..01f2b38daab3 100644 >>>> --- a/drivers/scsi/scsi_scan.c >>>> +++ b/drivers/scsi/scsi_scan.c >>>> @@ -1162,6 +1162,7 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget, >>>> blist_flags_t bflags; >>>> int res = SCSI_SCAN_NO_RESPONSE, result_len = 256; >>>> struct Scsi_Host *shost = dev_to_shost(starget->dev.parent); >>>> + struct request_queue *q; >>>> /* >>>> * The rescan flag is used as an optimization, the first scan of a >>>> @@ -1182,6 +1183,10 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget, >>>> *bflagsp = scsi_get_device_flags(sdev, >>>> sdev->vendor, >>>> sdev->model); >>>> + q = sdev->request_queue; >>>> + if (queue_max_hw_sectors(q) > shost->max_sectors) >>>> + blk_queue_max_hw_sectors(q, shost->max_sectors); >>>> + >>>> return SCSI_SCAN_LUN_PRESENT; >>>> } >>>> scsi_device_put(sdev); >>>> @@ -2006,4 +2011,3 @@ void scsi_forget_host(struct Scsi_Host *shost) >>>> } >>>> spin_unlock_irqrestore(shost->host_lock, flags); >>>> } >>>> - >>> >> > > -- Brian King Power Linux I/O IBM Linux Technology Center
