Re: [PATCH] Revert "virtio-scsi: Send "REPORTED LUNS CHANGED" sense data upon disk hotplug events"

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On Wed, Jul 12, 2023 at 12:14 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
>
> On Wed, Jul 12, 2023 at 10:06:56AM +0200, Paolo Bonzini wrote:
> >On 7/11/23 22:21, Mike Christie wrote:
> >>What was the issue you are seeing?
> >>
> >>Was it something like you get the UA. We retry then on one of the
> >>retries the sense is not setup correctly, so the scsi error handler
> >>runs? That fails and the device goes offline?
> >>
> >>If you turn on scsi debugging you would see:
> >>
> >>
> >>[  335.445922] sd 0:0:0:0: [sda] tag#15 Add. Sense: Reported luns data has changed
> >>[  335.445922] sd 0:0:0:0: [sda] tag#16 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>[  335.445925] sd 0:0:0:0: [sda] tag#16 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>[  335.445929] sd 0:0:0:0: [sda] tag#17 Done: FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> >>[  335.445932] sd 0:0:0:0: [sda] tag#17 CDB: Write(10) 2a 00 00 db 4f c0 00 00 20 00
> >>[  335.445934] sd 0:0:0:0: [sda] tag#17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>[  335.445936] sd 0:0:0:0: [sda] tag#17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>[  335.445938] sd 0:0:0:0: [sda] tag#17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>[  335.445940] sd 0:0:0:0: [sda] tag#17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>[  335.445942] sd 0:0:0:0: [sda] tag#17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>[  335.445945] sd 0:0:0:0: [sda] tag#17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>[  335.451447] scsi host0: scsi_eh_0: waking up 0/2/2
> >>[  335.451453] scsi host0: Total of 2 commands on 1 devices require eh work
> >>[  335.451457] sd 0:0:0:0: [sda] tag#16 scsi_eh_0: requesting sense
> >
> >Does this log come from internal discussions within Oracle?
> >
> >>I don't know the qemu scsi code well, but I scanned the code for my co-worker
> >>and my guess was commit 8cc5583abe6419e7faaebc9fbd109f34f4c850f2 had a race in it.
> >>
> >>How is locking done? when it is a bus level UA but there are multiple devices
> >>on the bus?
> >
> >No locking should be necessary, the code is single threaded.  However,
> >what can happen is that two consecutive calls to
> >virtio_scsi_handle_cmd_req_prepare use the unit attention ReqOps, and
> >then the second virtio_scsi_handle_cmd_req_submit finds no unit
> >attention (see the loop in virtio_scsi_handle_cmd_vq).  That can
> >definitely explain the log above.
>
> Yes, this seems to be the case!
> Thank you both for the help!
>
> Following Paolo's advice, I'm preparing a series for QEMU to solve the
> problem!

Series posted here:
https://lore.kernel.org/qemu-devel/20230712134352.118655-1-sgarzare@xxxxxxxxxx/

Stefano

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