Re: MFC fixes for uninitialized kernel stack variables in sys/cam or do direct fix for pvscsi driver
Date: Mon, 20 Jan 2025 12:48:47 UTC
> On Jan 15, 2025, at 12:37 PM, Warner Losh <imp@bsdimp.com> wrote: > > Great. This looks good. MFSing is done, along with the following commits those clear the stack allocated CCBs. 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 Everything looks good so far. Best regards, Zhenlei > > Warner > > On Tue, Jan 14, 2025, 9:36 PM Zhenlei Huang <zlei@freebsd.org <mailto:zlei@freebsd.org>> wrote: > > >> On Jan 13, 2025, at 5:06 PM, Zhenlei Huang <zlei@FreeBSD.org <mailto:zlei@FreeBSD.org>> wrote: >> >> >> >>> On Jan 13, 2025, at 4:22 PM, Zhenlei Huang <zlei@FreeBSD.org <mailto:zlei@FreeBSD.org>> wrote: >>> >>> >>> >>>> On Dec 28, 2024, at 6:03 AM, Warner Losh <imp@bsdimp.com <mailto: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 :) >> >> And the individual fix for pvscsi is posted to https://reviews.freebsd.org/D48438 <https://reviews.freebsd.org/D48438> . > > Landed in -current. Will be MFCed to stable/13 after a few days. > >> >>> >>> Best regards, >>> Zhenlei > > >