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

[Thomas Bogendoerfer <tsbogend@alpha.franken.de>]

On Wed, Mar 19, 2025 at 03:06:12PM +0100, Frederic Weisbecker wrote:
> Le Wed, Mar 19, 2025 at 12:07:07PM +0100, Thomas Bogendoerfer a écrit :
> > On Sat, Mar 15, 2025 at 08:40:02PM +0100, Marco Crivellari wrote:
> > > MIPS re-enables interrupts on its idle routine and performs
> > > a TIF_NEED_RESCHED check afterwards before putting the CPU to sleep.
> > > 
> > > The IRQs firing between the check and the 'wait' instruction may set the
> > > TIF_NEED_RESCHED flag. In order to deal with this possible race, IRQs
> > > interrupting __r4k_wait() rollback their return address to the
> > > beginning of __r4k_wait() so that TIF_NEED_RESCHED is checked
> > > again before going back to sleep.
> > > 
> > > However idle IRQs can also queue timers that may require a tick
> > > reprogramming through a new generic idle loop iteration but those timers
> > > would go unnoticed here because __r4k_wait() only checks
> > > TIF_NEED_RESCHED. It doesn't check for pending timers.
> > 
> > can you give a commit ID, when this change got introduced ?
> 
> That would be:
> 
>      Fixes: c65a5480ff29 ("[MIPS] Fix potential latency problem due to non-atomic cpu_wait.")

hmm, so even then checking TIF_NEED_RESCHED wasn't enough  (we are talking
about 2.6.27) ?

Thomas.

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