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Message-ID: <522b297a-7890-bf2d-fa08-2f0a20c848c7@huaweicloud.com>
Date: Wed, 5 Jul 2023 10:16:12 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Benjamin Block <bblock@...ux.ibm.com>,
Marc Hartmayer <mhartmay@...ux.ibm.com>
Cc: Yu Kuai <yukuai1@...weicloud.com>, linux-scsi@...r.kernel.org,
linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
yangerkun@...wei.com, hch@....de, chaitanyak@...dia.com,
shinichiro.kawasaki@....com, dgilbert@...erlog.com,
jejb@...ux.ibm.com, martin.petersen@...cle.com, axboe@...nel.dk,
"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] scsi/sg: don't grab scsi host module reference
Hi,
在 2023/07/05 2:51, Benjamin Block 写道:
> On Tue, Jul 04, 2023 at 07:04:00PM +0200, Marc Hartmayer wrote:
>> On Thu, Jun 22, 2023 at 12:01 AM +0800, Yu Kuai <yukuai1@...weicloud.com> wrote:
>>> From: Yu Kuai <yukuai3@...wei.com>
>>> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
>>> index 2433eeef042a..dcb73787c29d 100644
>>> --- a/drivers/scsi/sg.c
>>> +++ b/drivers/scsi/sg.c
>>> @@ -1497,7 +1497,7 @@ sg_add_device(struct device *cl_dev)
>>> int error;
>>> unsigned long iflags;
>>>
>>> - error = scsi_device_get(scsidp);
>>> + error = blk_get_queue(scsidp->request_queue);
>>> if (error)
>>> return error;
>>>
>
> Might be interesting as well. Marc showed me a `dmesg` snipped earlier
> from when the bind fails:
>
> [ 15.441817] scsi host2: scsi_eh_2: sleeping
> [ 15.441899] scsi_debug:sdebug_driver_probe: scsi_debug: trim poll_queues to 0. poll_q/nr_hw = (0/1)
> [ 15.441907] scsi host2: scsi_debug: version 0191 [20210520]
> dev_size_mb=8, opts=0x0, submit_queues=1, statistics=0
> [ 15.442078] scsi host2: scsi_scan_host_selected: <4294967295:4294967295:18446744073709551615>
> [ 15.442267] scsi 2:0:0:0: scsi scan: INQUIRY pass 1 length 36
> [ 15.442286] scsi 2:0:0:0: scsi scan: INQUIRY successful with code 0x0
> [ 15.442296] scsi 2:0:0:0: scsi scan: INQUIRY pass 2 length 96
> [ 15.442308] scsi 2:0:0:0: scsi scan: INQUIRY successful with code 0x0
> [ 15.442317] scsi 2:0:0:0: Direct-Access Linux scsi_debug 0191 PQ: 0 ANSI: 7
> [ 15.442554] scsi 2:0:0:0: Power-on or device reset occurred
> [ 15.442560] scsi 2:0:0:0: tag#50 Done: SUCCESS Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> [ 15.442565] scsi 2:0:0:0: tag#50 CDB: Report supported operation codes a3 0c 01 88 00 00 00 00 00 14 00 00
> [ 15.442569] scsi 2:0:0:0: tag#50 Sense Key : Unit Attention [current]
> [ 15.442573] scsi 2:0:0:0: tag#50 Add. Sense: Power on occurred
>
> The bind should happend around here somewhere I think.
>
> [ 15.472680] sd 2:0:0:0: scsi scan: Sending REPORT LUNS to (try 0)
> [ 15.472703] sd 2:0:0:0: scsi scan: REPORT LUNS successful (try 0) result 0x0
> [ 15.472706] sd 2:0:0:0: scsi scan: REPORT LUN scan
> [ 15.472709] sd 2:0:0:0: scsi scan: device exists on 2:0:0:0
> [ 15.492874] sd 2:0:0:0: [sdi] 16384 512-byte logical blocks: (8.39 MB/8.00 MiB)
> [ 15.502853] sd 2:0:0:0: [sdi] Write Protect is off
> [ 15.502856] sd 2:0:0:0: [sdi] Mode Sense: 73 00 10 08
> [ 15.522819] sd 2:0:0:0: [sdi] Write cache: enabled, read cache: enabled, supports DPO and FUA
> [ 15.552773] sd 2:0:0:0: [sdi] Preferred minimum I/O size 512 bytes
> [ 15.552776] sd 2:0:0:0: [sdi] Optimal transfer size 524288 bytes
> [ 15.575373] sd 2:0:0:0: [sdi] tag#62 Done: SUCCESS Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> [ 15.575377] sd 2:0:0:0: [sdi] tag#62 CDB: Inquiry 12 01 b9 00 04 00
> [ 15.575380] sd 2:0:0:0: [sdi] tag#62 Sense Key : Illegal Request [current]
> [ 15.575383] sd 2:0:0:0: [sdi] tag#62 Add. Sense: Invalid field in cdb
> [ 15.645749] sd 2:0:0:0: [sdi] Attached SCSI disk
>
> But we don't even see the `sg_alloc: dev=...` message that is logged in
> `sg_alloc()`. And between the change above and the call to `sg_alloc()`,
> there is only the character device allocation; and if that failed, it
> would print an error. So either the bind is never even tried, or the new
> `blk_get_queue()` fails to get a reference.
> Which is odd, since the only way that would happen is, if the queue
> was marked dying; but we see that the stack is using it for LUN probing
> in `sd`.
Yes, if scsi_device_get() works fine, but blk_get_queue() has problems,
it seems to me that sg_add_device() can be called with scsi_device queue
mark dying? This is odd, but I'm not sure if it's the case.
Thanks,
Kuai
>
>> This change (bisected) triggers a regression in our KVM on s390x CI. The
>> symptom is that a “scsi_debug device” does not bind to the scsi_generic
>> driver. On s390x you can reproduce the problem as follows (I have not
>> tested on x86):
>>
>> With this patch applied:
>>
>> $ sudo modprobe scsi_debug
>
> One more thing maybe worth mentioning: in the kernel configuration we
> use in the CI we have `sg` built-in. I guess most have it built as
> module.
>
>> $ # Get the 'scsi_host,channel,target_number,LUN' tuple for the scsi_debug device
>> $ lsscsi |grep scsi_debug |awk '{ print $1 }'
>> [0:0:0:0]
>> $ sudo stat /sys/bus/scsi/devices/0:0:0:0/scsi_generic
>> stat: cannot statx '/sys/bus/scsi/devices/0:0:0:0/scsi_generic': No such file or directory
>>
>>
>> Patch reverted:
>>
>> $ sudo modprobe scsi_debug
>> $ lsscsi |grep scsi_debug |awk '{ print $1 }'
>> [0:0:0:0]
>> $ sudo stat /sys/bus/scsi/devices/0:0:0:0/scsi_generic
>> File: /sys/bus/scsi/devices/0:0:0:0/scsi_generic
>> Size: 0 Blocks: 0 IO Block: 4096 directory
>> Device: 0,20 Inode: 12155 Links: 3
>> …
>
> That's all I got from looking at it earlier, so far.
>
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