Re: [RFC PATCH] zram: avoid preemption with CPU-based compression backends

[Sergey Senozhatsky]

Hello,

On (26/08/14 08:07), Barry Song wrote:
> > On (26/08/05 08:55), Barry Song (Xiaomi) wrote:
> > > @@ -128,14 +128,20 @@ struct zcomp_strm *zcomp_stream_get(struct zcomp *comp)
> > >                * so then unlock and re-try on the current CPU.
> > >                */
> > >               mutex_lock(&zstrm->lock);
> > > +             if (!comp->ops->async && !IS_ENABLED(CONFIG_PREEMPT_RT))
> > > +                     preempt_disable();
> >
> > We take slot_lock(), which is preemptible, under stream lock on
> > some paths.
> 
> Hi Sergey,
> 
> As promised in [1], those patches are still under testing on real
> Android phones. However, I'm quite curious which path takes
> slot_lock while holding the zstream lock

Oh, I think you are right.  We do the opposite: stream lock under
slot lock, and we also do the stream lock -> zsmalloc lock/unlock -> stream
unlock -> slot lock/unlock chain.  But it doesn't look like we ever
do stream lock -> slot lock, you are right.  Sorry for the confusion.