svn commit: r238907 - projects/calloutng/sys/kern

[Attilio Rao]

On Sun, Sep 9, 2012 at 8:15 PM, John Baldwin <jhb at freebsd.org> wrote:
> On 9/9/12 11:03 AM, Attilio Rao wrote:
>> On 8/2/12, Attilio Rao <attilio at freebsd.org> wrote:
>>> On 7/30/12, John Baldwin <jhb at freebsd.org> wrote:
>>
>> [ trimm ]
>>
>>>> --- //depot/projects/smpng/sys/kern/subr_turnstile.c        2012-06-04
>>>> 18:27:32.000000000 0000
>>>> +++ //depot/user/jhb/lock/kern/subr_turnstile.c     2012-06-05
>>>> 00:27:57.000000000 0000
>>>> @@ -684,6 +684,7 @@
>>>>     if (owner)
>>>>             MPASS(owner->td_proc->p_magic == P_MAGIC);
>>>>     MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
>>>> +   KASSERT(!TD_IS_IDLETHREAD(td), ("idle threads cannot block on locks"));
>>>>
>>>>     /*
>>>>      * If the lock does not already have a turnstile, use this thread's
>>>
>>> I'm wondering if we should also use similar checks in places doing
>>> adaptive spinning (including the TD_NO_SLEEPING check). Likely yes.
>>
>> So what do you think about this?
>
> This is isn't really good enough then.  An idle thread should not
> acquire any lock that isn't a spin lock.  Instead, you would be
> better off removing the assert I added above and adding an assert to
> mtx_lock(), rw_{rw}lock(), sx_{sx}lock(), lockmgr(), rm_{rw}lock() and
> all the try variants of those.

While this is true, I thought about this route but I didn't want to go
for it because it would pollute much more code than the current
approach + patch I proposed, which would enough to find offending
cases.
I'm not sure I want to pollute all the kernel locking with checks for
idlethread, yet I think the current code is not complete and thus I
still think my patch is a reasonable compromise.

Attilio


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