Hello,
On Thu, Apr 22, 2021 at 03:08:21PM +0200, Mark Kettenis wrote:
> > Date: Thu, 22 Apr 2021 14:43:24 +0200
> > From: Alexandr Nedvedicky <[email protected]>
> >
> > Hello,
> >
> > On Thu, Apr 22, 2021 at 01:09:34PM +0200, Alexander Bluhm wrote:
> > > On Thu, Apr 22, 2021 at 12:33:13PM +0200, Hrvoje Popovski wrote:
> > > > r620-1# papnpaiancini:cc :p :op
> > > > opooolo_llc_ac_caccahhceh_ei_eti_tieetmme_mm__amgamigacigci__cc_hccehhcekcekc::
> > > > k :m bmubmfubfuppflp llc pc pcuup uf rfferree eel el iilsitss tm tom
> > > > omddoidfiiifeifeidde:d ::i ti etietmme m
> > > > a daddardd rd0 r0
> > > > xx0fxfffffffffffffddf88d08c0cc0c6c76afc9b3f04500400++01+61 610 6x0
> > > > fx0fxffffffffffdffdf88d08
> > > > 00020720d72a8c0049703eb!ef!e==!0=x009x59x95995b9ebbaee3ae3ae344ef54f5a4bff7db07990a9
> > >
> > > Wow. 3 CPUs panic in pool_cache_get() pool_cache_item_magic_check
> > > simultaneously. This makes me think we may have a bug there.
> > >
> >
> > I took a look at arch/amd64/include/intrdefs.h where interrupt
> > priorities are defined.
> >
> > IPL_NET has priority set to 7,
> > IPL_SOFTNET has higher priority set 5
> >
> > all allocations are coming from mbpool via m_gethdr(), interrupt
> > level priority for mbpool is set to IPL_NET. If I understand
> > code in m_pool_get() right, then the pool_cache_enter() does not
> > stop guys who call m_gethdr() with IPL_SOFTNET.
> >
> > if we put KERNEL_LOCK() there the problem is gone, mostlikely
> > because the IPL_SOFTNET guy waits for KERNEL_LOCK therefore it
> > can not interfere with our IPL_NET task, which forwards packet.
> >
> > I admit it's a poor speculation, I have no 'hard proof' for my
> > claim here. So I might be very wrong here.
>
> Not sure what you are trying to say here, but IPL_SOFTNET is lower
> than IPL_NET. So code that runs at IPL_SOFTNET will raise the IPL to
> IPL_NET in pool_cache_enter(), blocking IPL_NET interrupts until
> pool_cache_leave() is called and the IPL is lowered again to
> IPL_SOFTNET.
>
> I'm fairly confident the "normal" pools are mpsafe; we have been using
> those in concurrent contexts without holding the kernel lock for a
> long time already. But the pool cache layer is still relatively new...
my understanding was twisted: lower the number the higher the priority.
this made me thinking IPL_NET won't prevent processes running with
IPL_SOFTNET from running into pool_cache_enter()/pool_cache_leave()
section.
thanks and
regards
sashan
