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

[Attilio Rao]

On 7/30/12, Attilio Rao <attilio at freebsd.org> wrote:
> On 7/30/12, Konstantin Belousov <kostikbel at gmail.com> wrote:
>> On Mon, Jul 30, 2012 at 03:24:26PM +0100, Attilio Rao wrote:
>>> On 7/30/12, Davide Italiano <davide at freebsd.org> wrote:
>>> > On Mon, Jul 30, 2012 at 4:02 PM, Attilio Rao <attilio at freebsd.org>
>>> > wrote:
>>> > Thanks for the comment, Attilio.
>>> > Yes, it's exactly what you thought. If direct flag is equal to one
>>> > you're sure you're processing a callout which runs directly from
>>> > hardware interrupt context. In this case, the running thread cannot
>>> > sleep and it's likely you have TDP_NOSLEEPING flags set, failing the
>>> > KASSERT() in THREAD_NO_SLEEPING() and leading to panic if kernel is
>>> > compiled with INVARIANTS.
>>> > In case you're running from SWI context (direct equals to zero) code
>>> > remains the same as before.
>>> > I think what I'm doing works due the assumption thread running never
>>> > sleeps. Do you suggest some other way to handle this?
>>>
>>> Possibly the quicker way to do this is to have a way to deal with the
>>> TDP_NOSLEEPING flag in recursed way, thus implement the same logic as
>>> VFS_LOCK_GIANT() does, for example.
>>> You will need to change the few callers of THREAD_NO_SLEEPING(), but
>>> the patch should be no longer than 10/15 lines.
>>
>> There are already curthread_pflags_set/restore KPI designed exactly to
>> handle
>> nested private thread flags.
>
> Yes, however I would use curthread_pflags* KPI within
> THREAD_NO_SLEEPING() as this name is much more explicit.
>
>> Also, I wonder, should you assert somehow that direct dispatch cannot
>> block
>> as well ?
>
> Yes, it would be optimal, but I don't think we have a flag for that
> right now, do we?

More explicitly, I think such combination TDP_NOSLEEPING +
TDP_NOBLOCKING (name invented) should be set on entering the interrupt
context, not only related to this part of callouts. This would be a
very good help for catching buggy situations.

Attilio


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