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

> On Dec 28, 2024, at 6:03 AM, Warner Losh <imp@bsdimp.com> wrote:
> 
> 
> 
> On Mon, Dec 2, 2024 at 2:41 AM Zhenlei Huang <zlei@freebsd.org <mailto:zlei@freebsd.org>> wrote:
> 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.
> 
> 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.

That is clear.

> 
> 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.
>  
> Which one do you prefer, MFC commits to stable/13, or do direct fix for pvscsi driver to stable/13 ?
> 
> [[ Sorry for the delay, I missed this all month ]]
> 
> I generally prefer a MFC, unless the code is no longer in -current.

The code live in -current and all supported stable branches.

> 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.

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.

> 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.

Do you mean the `cherry picked from commit` commit message ?

> 
> Warner


I'm preparing and testing the MFCing. Bless me to not make things messed up :)

Best regards,
Zhenlei