Questions about locking; turnstiles and sleeping threads

[Alfred Perlstein]

OK that makes more sense.

I've cc'd Hans for the usb issue.

On 11/13/14, 1:38 AM, Adrian Chadd wrote:
> It looks like the initial firings are because the check I put in
> didn't check to see if it's MPSAFE.
>
> eg:
>
> ip6_input -> tcp6_input -> tcp_input -> tcp_do_segment ->
> tcp_timer_active -> callout_stop_safe; called with tcpinp held.
> closefp() -> closef() -> fdrop -> soclose() -> sofree() ->
> tcp_usr_detach() -> tcp_discardcb() -> callout_stop_safe() with the
> tcpinp and tcp locks held.
> ioctl -> sys_ioctl-> devfs_ioctl_f -> acpi_ackSleepState ->
> callout_stop_safe; with ACPI global lock held;
> suspend path -> hdaa_suspend -> callout_stop_safe() with HDA driver mutex held
>
> So we can't just put the simple witness check from _sleep() in
> _callout_stop_safe(), it looks like it's mis-firing on MPSAFE callouts
> (which the tcp timers all are) and that won't go via the sleepq.
> It looks like the acpi callout is also mpsafe, as well as the HDA jack callout.
>
> However, I did pick up this:
>
> detach path -> usbd_transfer_drain() -> usbd_transfer_stop() ->
> ehci_device_intr_close() -> usbd_transfer_done() ->
> callout_stop_safe() with USB HUB mutex held
>
> The usbd_transfer_done() callout is initialised with a mutex, but the
> witness code should've detected it wasn't callout->c_lock and thus
> warned.
>
>
>
> -adrian
>
> On 13 November 2014 01:13, Alfred Perlstein <alfred at freebsd.org> wrote:
>> On 11/13/14, 1:09 AM, Adrian Chadd wrote:
>>> On 13 November 2014 00:59, Alfred Perlstein <alfred at freebsd.org> wrote:
>>>> On 11/12/14, 11:25 PM, Adrian Chadd wrote:
>>>>> On 12 November 2014 19:48, Adrian Chadd <adrian at freebsd.org> wrote:
>>>>>> kan pointed out that we should likely do a WITNESS_WARN() in the
>>>>>> relevant spots in the callout code so we catch these before it
>>>>>> happens.
>>>>>>
>>>>>> I'll see what we can add to -HEAD to be pro-active about it.
>>>>> Amusingly, I tried adding it and it made my laptop turn to soup very
>>>>> quickly - among other things, the TCP timer callouts are all setup
>>>>> with non sleep locks held.
>>>>>
>>>> Howso?  You only have to worry about callout_drain(), most other callout
>>>> functions should be safe-ish....
>>> yeah, except for all the places where they drain the timer once
>>> something happens so it doesn't fire.
>>>
>>> :)
>>
>> What is the backtrace...?
>>
>>
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