Re: MFC fixes for uninitialized kernel stack variables in sys/cam or do direct fix for pvscsi driver

Great. This looks good.

Warner

On Tue, Jan 14, 2025, 9:36 PM Zhenlei Huang <zlei@freebsd.org> wrote:

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> On Jan 13, 2025, at 5:06 PM, Zhenlei Huang <zlei@FreeBSD.org> wrote:
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> On Jan 13, 2025, at 4:22 PM, Zhenlei Huang <zlei@FreeBSD.org> wrote:
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> On Dec 28, 2024, at 6:03 AM, Warner Losh <imp@bsdimp.com> wrote:
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> On Mon, Dec 2, 2024 at 2:41 AM Zhenlei Huang <zlei@freebsd.org> wrote:
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>> Hi Warner,
>>
>> Recently I upgraded some ESXi vms from 13.3 to 13.4 and noticed weird
>> report for sas speed.
>> The boot console has the following,
>>
>> ```
>> da0 at pvscsi0 bus 0 scbus2 target 0 lun 0
>> da0: <VMware Virtual disk 2.0> Fixed Direct Access SPC-4 SCSI device
>> da0: 4294967.295MB/s transfers
>> ```
>> But camcontrol report the correct value,
>> ```
>> # camcontrol inquiry da0 -R
>> pass1: 750.000MB/s transfers, Command Queueing Enabled
>> ```
>>
>> The `4294967.295MB` is actually 0xffff_ffff or -1 but I do not see any
>> logic set those values.
>>
>> Finally I managed to get the stack trace,
>> ```
>> _scsi_announce_periph
>> scsi_announce_periph_sbuf
>> xpt_announce_periph_sbuf
>> dadone_proberc
>> xpt_done_process
>> xpt_done_td
>> fork_exit
>> fork_trampoline
>> ```
>>
>> and noticed that the last param `cts` of `_scsi_announce_periph(struct
>> cam_periph *periph, u_int *speed, u_int *freq, struct ccb_trans_settings
>> *cts)`
>> is from kernel stack and is not properly initialized, latter I found some
>> commits related to this,
>>
>> 076686fe0703 cam: make sure to clear CCBs allocated on the stack
>> ec5325dbca62 cam: make sure to clear even more CCBs allocated on the stack
>> 0f206cc91279 cam: add missing zeroing of a stack-allocated CCB.
>> 616a676a0535 cam: clear stack-allocated CCB in the target layer
>>
>> I applied them to stable/13, rebuild and reboot, now the speed of da0 is
>> reported correctly. I also tried to patch the pvscsi driver with few lines
>> and
>> it also works as intended.
>>
>> ```
>> --- a/sys/dev/vmware/pvscsi/pvscsi.c
>> +++ b/sys/dev/vmware/pvscsi/pvscsi.c
>> @@ -1444,6 +1444,10 @@ pvscsi_action(struct cam_sim *sim, union ccb *ccb)
>>                 cts->proto_specific.scsi.flags = CTS_SCSI_FLAGS_TAG_ENB;
>>                 cts->proto_specific.scsi.valid = CTS_SCSI_VALID_TQ;
>>
>> +               /* Prefer connection speed over sas port speed */
>> +               /* cts->xport_specific.sas.bitrate = 0; */
>> +               cts->xport_specific.sas.valid = 0;
>> +
>>                 ccb_h->status = CAM_REQ_CMP;
>>                 xpt_done(ccb);
>> ```
>>
>> Things come clear and I know why this weird speed happens, now it is time
>> to decide how to fix it.
>>
>> Fixing the consumer of cam, aka pvscsi driver, is quite simple and
>> promising. I did a quick search it appears other consumers set
>> `cts->xport_specific.sas.valid` correctly. It does not convince me as I'm
>> quite new to cam subsystem.
>>
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> Yes. sas.valid is set when the sas.bitrate and other data has been set
> correctly. Setting it to 0 like this ensures it's ignored.  So if you know
> the speed, set sas.bitrate to that speed and sas.valid to 1.
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> That is clear.
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> I'm not sure I answered the question right, but if not, please clarify or
> point out what I missed and I'll try again.
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>> Which one do you prefer, MFC commits to stable/13, or do direct fix for
>> pvscsi driver to stable/13 ?
>>
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> [[ Sorry for the delay, I missed this all month ]]
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> I generally prefer a MFC, unless the code is no longer in -current.
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> The code live in -current and all supported stable branches.
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> Even if there's two different fixes for this logical bug, fixing it in
> current, then MFCing that (with the current hash) is fine, even if the
> stable/13 changes are completely different.
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> The bug does not exist in current and stable/14 but only in stable/13, due
> to Edward's work ( commits those zero stack-allocated CCBs ) were not MFCed
> into stable/13 branch.
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> For stable/13 I guess it matters a bit less than stable/14 since I'll be
> merging to it less, but if it's a commit from -current that doesn't need to
> be made to -stable because of the new commit on stable, I tend to include
> the MFC hash text.
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> Do you mean the `cherry picked from commit` commit message ?
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> Warner
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> I'm preparing and testing the MFCing. Bless me to not make things messed
> up :)
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> And the individual fix for pvscsi is posted to
> https://reviews.freebsd.org/D48438 .
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> Landed in -current. Will be MFCed to stable/13 after a few days.
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> Best regards,
> Zhenlei
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