2015-10-15 16:22 GMT+08:00 Zhengping Zhou <johnzzpcrystal@xxxxxxxxx>:
> Yes
>
> But it's interesting ,when you continue to add this device (with the
> same LUN, target, bus, and host number!) to the list,scsi_add_device
> will call scsi_probe_and_add_lun,and it will call
> scsi_device_lookup_by_target(starget, lun) to recheck its existence
> finally.but scsi_device_lookup_by_target doesn't has the problem what
> I mentioned in this patch .So it's OK when you add this device again.
>
> Forgive my poor English!
> 2015-10-15 15:53 GMT+08:00 Hannes Reinecke <hare@xxxxxxx>:
>> On 10/15/2015 09:38 AM, Zhengping Zhou wrote:
>>> when a scsi_device is unpluged from scsi controller, if the
>>> scsi_device is still be used by application layer,it won't be
>>> released until users release it. In this case, scsi_device_remove just set
>>> the scsi_device's state to be SDEV_DEL. But if you plug the disk
>>> just before the old scsi_device is released, then there will be two
>>> scsi_device structures in scsi_host->__devices. when the next unpluging
>>> event happens,some low-level drivers will check whether the scsi_device
>>> has been added to host (for example, the megaraid sas series controller)
>>> by calling scsi_device_lookup(call __scsi_device_lookup).
>>> __scsi_device_lookup will return the first scsi_device. Because its
>>> state is SDEV_DEL, the scsi_device_lookup will return NULL finally,
>>> making the low-level driver assume that the scsi_device has been
>>> removed,and won't call scsi_device_remove,which will lead the
>>> failure of hot swap.
>>> Signed-off-by: Zhengping Zhou <johnzzpcrystal@xxxxxxxxx>
>>> ---
>>> Hi all:
>>> I'm sorry to bother again,that's my second time to send
>>> this patch.
>>> I find a bug about the failure of hot swap when I am using
>>> megaraid sas series controller. Finally I have found that
>>> when controller receives the event of hot swap, it will firstly
>>> check whether the device is added to the system/host by calling
>>> scsi_device_lookup.The logics in function megasas_aen_polling
>>> is as follows:
>>> case MR_EVT_PD_REMOVED:
>>> if (megasas_get_pd_list(instance) == 0) {
>>> for (i = 0; i < MEGASAS_MAX_PD_CHANNELS; i++) {
>>> for (j = 0;
>>> j < MEGASAS_MAX_DEV_PER_CHANNEL;
>>> j++) {
>>>
>>> pd_index =
>>> (i * MEGASAS_MAX_DEV_PER_CHANNEL) + j;
>>>
>>> sdev1 = scsi_device_lookup(host, i, j, 0);
>>>
>>> if (instance->pd_list[pd_index].driveState
>>> == MR_PD_STATE_SYSTEM) {
>>> if (sdev1)
>>> scsi_device_put(sdev1);
>>> } else {
>>> if (sdev1) {
>>> scsi_remove_device(sdev1);
>>> scsi_device_put(sdev1);
>>> }
>>> }
>>> }
>>> }
>>> }
>>> If the previous scsi_device is not released, this will lead the
>>> appearance of two scsi_devices which correspond with the same disk.
>>> And when the disk is unpluged afterwards, the controller will assume
>>> that this disk has never been added into the system/host. Thus it won't
>>> call scsi_device_remove. When I finish this modification, this problem
>>> is fixed.So far, I have successfully test PCI_DEVICE_ID_LSI_SAS0073SKINNY
>>> and PCI_DEVICE_ID_LSI_FURY.
>>> Thanks
>>> Zhengping
>>> ---
>>> drivers/scsi/scsi.c | 2 ++
>>> 1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
>>> index 207d6a7..5251d6d 100644
>>> --- a/drivers/scsi/scsi.c
>>> +++ b/drivers/scsi/scsi.c
>>> @@ -1118,6 +1118,8 @@ struct scsi_device *__scsi_device_lookup(struct Scsi_Host *shost,
>>> struct scsi_device *sdev;
>>>
>>> list_for_each_entry(sdev, &shost->__devices, siblings) {
>>> + if (sdev->sdev_state == SDEV_DEL)
>>> + continue;
>>> if (sdev->channel == channel && sdev->id == id &&
>>> sdev->lun ==lun)
>>> return sdev;
>>>
>> Ho-hum.
>>
>> So lookup will return NULL, which then will cause the subsequent
>> functions to assume the scsi_device is not present, right?
>>
>> And if you're _really_ unlucky it'll continue to add this device
>> (with the same LUN, target, bus, and host number!) to the list,
>> resulting in us having _two_ devices with the same number on the list.
>>
>> Happy lookup.
>>
>> I guess this calls for the lock rework from Johannes ...
>>
>> Cheers,
>>
>> Hannes
>> --
>> Dr. Hannes Reinecke zSeries & Storage
>> hare@xxxxxxx +49 911 74053 688
>> SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
>> GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
>> HRB 21284 (AG Nürnberg)
You can compare the function __scsi_device_lookup_by_target and the
function __scsi_device_lookup.
It will be more easy to figure out this patch.
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