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

[Attilio Rao]

On Mon, Jul 30, 2012 at 4:49 PM, John Baldwin <jhb at freebsd.org> wrote:
> On Monday, July 30, 2012 10:39:43 am Konstantin Belousov 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.
>>
>> Also, I wonder, should you assert somehow that direct dispatch cannot block
>> as well ?
>
> Hmm, I have a nested TDP_NOSLEEPING already (need it to fix an issue in
> rmlocks).  It uses a count though as the flag is set during rm_rlock() and
> released during rm_runlock().  I don't think it could use a set/restore KPI as
> there is no good place to store the state.

Our stock rmlocks don't seem to use TDP_NOSLEEPING/THREAD_NO_SLEEPING
so I'm not entirely sure about the case you were trying to fix, can
you show the patch?

Thanks,
Attilio


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