Re: struct ifnet and ifaddr handling [was: Re: Making global variables of if.c MPSAFE]

[Masao Uebayashi <uebayasi%gmail.com@localhost>]

On Tue, Nov 25, 2014 at 12:48 AM, Taylor R Campbell
<campbell+netbsd-tech-kern%mumble.net@localhost> wrote:
>    Date: Tue, 25 Nov 2014 00:42:58 +0900
>    From: Masao Uebayashi <uebayasi%gmail.com@localhost>
>
>    On Mon, Nov 24, 2014 at 11:16 PM, Taylor R Campbell
>    <campbell+netbsd-tech-kern%mumble.net@localhost> wrote:
>    >    Date: Mon, 24 Nov 2014 15:26:21 +0900
>    >    From: Masao Uebayashi <uebayasi%gmail.com@localhost>
>    >
>    >    I think pserialize_read_{enter,exit}() should explicitly call
>    >    KPREEMPT_{DISABLE,ENABLE}(), as is done in percpu_{getref,putref}().
>    >
>    > Not necessary -- splsoftserial is sufficient to prevent switching, and
>    > is necessary to block the pserialize cross-call until the reader is
>    > finished.
>
>    I want stronger constraint than softint context.  Softint prevents
>    threads from being preempted implicitly, but still allows to sleep.  I
>    want pserialize(9)'ed readers to never sleep (critical section).
>    KPREEMPT_DISABLE() (and kpreempt_disable()) sets l_noprempt.  Which
>    seems the official way to declare entering critical section.
>
> Different kinds of critical section.  Neither one actually prevents
> sleep.  It would be nice if pserialize_read and percpu communicated
> with ASSERT_SLEEPABLE, but that's not the case right now.

Right, I misread assertions in mi_switch()....

Maybe separating l_nopreempt into that of internal (scheduler) reason
and anything else helps?