linux-kernel - Re: [PATCH v6 1/1] MIPS: Fix idle VS timer enqueue

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Message-ID: <CAAofZF7XPm+tzPpwAPu0oDZem+EOVY18oAbVwAXzkGmtstnBQg@mail.gmail.com>
Date: Thu, 20 Mar 2025 09:44:23 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: Frederic Weisbecker <frederic@...nel.org>, linux-mips@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Anna-Maria Behnsen <anna-maria@...utronix.de>, 
	Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, 
	Huacai Chen <chenhuacai@...nel.org>, "Maciej W . Rozycki" <macro@...am.me.uk>
Subject: Re: [PATCH v6 1/1] MIPS: Fix idle VS timer enqueue

Hi,

yesterday I made this changes:

@@ -128,7 +128,11 @@ LEAF(__r4k_wait)
        */
       wait
       /* End of idle interrupt region. */
-1:
+SYM_INNER_LABEL(__r4k_wait_exit, SYM_L_LOCAL)
+       /* Check idle interrupt region size. */
+       .ifne   __r4k_wait_exit - __r4k_wait - 36
+       .error  "Idle interrupt region size mismatch: expected 36 bytes."
+       .endif
       jr      ra
        nop
       .set    pop
@@ -139,7 +143,7 @@ LEAF(__r4k_wait)
       .set    push
       .set    noat
       MFC0    k0, CP0_EPC
-       PTR_LA  k1, 1b
+       PTR_LA  k1, __r4k_wait_exit
       /* 36 byte idle interrupt region. */
       ori     k0, 0x1f
       PTR_ADDIU       k0, 5


Would it be ok to have the check done in this way?

Thanks


On Wed, Mar 19, 2025 at 11:09 PM Thomas Bogendoerfer
<tsbogend@...ha.franken.de> wrote:
>
> On Wed, Mar 19, 2025 at 03:43:13PM +0100, Frederic Weisbecker wrote:
> > > >   .set    MIPS_ISA_ARCH_LEVEL_RAW
> > > > + /*
> > > > +  * If an interrupt lands here, between enabling interrupts above and
> > > > +  * going idle on the next instruction, we must *NOT* go idle since the
> > > > +  * interrupt could have set TIF_NEED_RESCHED or caused a timer to need
> > > > +  * resched. Fall through -- see rollback_handler below -- and have
> > > > +  * the idle loop take care of things.
> > > > +  */
> > > >   wait
> > > > - /* end of rollback region (the region size must be power of two) */
> > > > + /* End of idle interrupt region. */
> > > >  1:
> > >
> > > please give this label a name for example __r4k_wait_exit and do a
> > > runtime check that it really has 36 bytes offset to __r4k_wait
> >
> > Where would be the best place for that?
> >
> > arch/mips/kernel/setup.c:setup_arch() maybe?
>
> scratch runtime check, a compile check is what I wanted to write...
>
> something like
>
> .if ((__r4k_wait_exit - __r4k_wait) != 36)
> .err
> .endif
>
> Thomas.
>
> --
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]



-- 

Marco Crivellari

L3 Support Engineer, Technology & Product




marco.crivellari@...e.com