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From: Ulf Hansson <ulf.hansson@linaro.org>
Date: Wed, 31 Jan 2024 13:26:22 +0100
Message-ID: <CAPDyKFoYJH4GLpFb6i1HsQSTpfxhHea16o0fwVReP7nfYftNeQ@mail.gmail.com>
Subject: Re: [PATCH] pmdomain: arm: Fix NULL dereference on scmi_perf_domain removal
To: Sudeep Holla <sudeep.holla@arm.com>
Cc: Cristian Marussi <cristian.marussi@arm.com>, linux-arm-kernel@lists.infradead.org, 
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"

On Wed, 31 Jan 2024 at 12:53, Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> On Wed, Jan 31, 2024 at 12:35:56PM +0100, Ulf Hansson wrote:
> > On Tue, 30 Jan 2024 at 21:07, Cristian Marussi <cristian.marussi@arm.com> wrote:
> > >
> > > On Tue, Jan 30, 2024 at 02:09:20PM +0100, Ulf Hansson wrote:
> > > > On Thu, 25 Jan 2024 at 20:18, Cristian Marussi <cristian.marussi@arm.com> wrote:
> > > > >
> > > > > On unloading of the scmi_perf_domain module got the below splat, when in
> > > > > the DT provided to the system under test the '#power-domain-cells' property
> > > > > was missing.
> > > > > Indeed, this particular setup causes the probe to bail out early without
> > > > > giving any error, so that, then, the removal code is run on unload, but
> > > > > without all the expected initialized structures in place.
> > > > >
> > > > > Add a check and bail out early on remove too.
> > > >
> > > > Thanks for spotting this!
> > > >
> > > > >
> > > > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
> > > > > Mem abort info:
> > > > >    ESR = 0x0000000096000004
> > > > >    EC = 0x25: DABT (current EL), IL = 32 bits
> > > > >    SET = 0, FnV = 0
> > > > >    EA = 0, S1PTW = 0
> > > > >    FSC = 0x04: level 0 translation fault
> > > > >  Data abort info:
> > > > >    ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
> > > > >    CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> > > > >    GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> > > > >  user pgtable: 4k pages, 48-bit VAs, pgdp=00000001076e5000
> > > > >  [0000000000000008] pgd=0000000000000000, p4d=0000000000000000
> > > > >  Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
> > > > >  Modules linked in: scmi_perf_domain(-) scmi_module scmi_core
> > > > >  CPU: 0 PID: 231 Comm: rmmod Not tainted 6.7.0-00084-gb4b1f27d3b83-dirty #15
> > > > >  Hardware name: linux,dummy-virt (DT)
> > > > >  pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> > > > >  pc : scmi_perf_domain_remove+0x28/0x70 [scmi_perf_domain]
> > > > >  lr : scmi_perf_domain_remove+0x28/0x70 [scmi_perf_domain]
> > > > >  sp : ffff80008393bc10
> > > > >  x29: ffff80008393bc10 x28: ffff0000875a8000 x27: 0000000000000000
> > > > >  x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
> > > > >  x23: ffff00008030c090 x22: ffff00008032d490 x21: ffff80007b287050
> > > > >  x20: 0000000000000000 x19: ffff00008032d410 x18: 0000000000000000
> > > > >  x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
> > > > >  x14: 8ba0696d05013a2f x13: 0000000000000000 x12: 0000000000000002
> > > > >  x11: 0101010101010101 x10: ffff00008510cff8 x9 : ffff800080a6797c
> > > > >  x8 : 0101010101010101 x7 : 7f7f7f7f7f7f7f7f x6 : fefefeff6364626d
> > > > >  x5 : 8080808000000000 x4 : 0000000000000020 x3 : 00000000553a3dc1
> > > > >  x2 : ffff0000875a8000 x1 : ffff0000875a8000 x0 : ffff800082ffa048
> > > > >  Call trace:
> > > > >   scmi_perf_domain_remove+0x28/0x70 [scmi_perf_domain]
> > > > >   scmi_dev_remove+0x28/0x40 [scmi_core]
> > > > >   device_remove+0x54/0x90
> > > > >   device_release_driver_internal+0x1dc/0x240
> > > > >   driver_detach+0x58/0xa8
> > > > >   bus_remove_driver+0x78/0x108
> > > > >   driver_unregister+0x38/0x70
> > > > >   scmi_driver_unregister+0x28/0x180 [scmi_core]
> > > > >   scmi_perf_domain_driver_exit+0x18/0xb78 [scmi_perf_domain]
> > > > >   __arm64_sys_delete_module+0x1a8/0x2c0
> > > > >   invoke_syscall+0x50/0x128
> > > > >   el0_svc_common.constprop.0+0x48/0xf0
> > > > >   do_el0_svc+0x24/0x38
> > > > >   el0_svc+0x34/0xb8
> > > > >   el0t_64_sync_handler+0x100/0x130
> > > > >   el0t_64_sync+0x190/0x198
> > > > >  Code: a90153f3 f9403c14 f9414800 955f8a05 (b9400a80)
> > > > >  ---[ end trace 0000000000000000 ]---
> > > > >
> > > > > Cc: Sudeep Holla <sudeep.holla@arm.com>
> > > > > Cc: Ulf Hansson <ulf.hansson@linaro.org>
> > > > > Fixes: 2af23ceb8624 ("pmdomain: arm: Add the SCMI performance domain")
> > > > > Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> > > > > ---
> > > > > I suppose the probe does NOT bail out with an error because this DT config has
> > > > > to be supported, right ?
> > > >
> > > > Actually, no. It's a mistake by me, the probe should bail out with an
> > > > error code.
> > > >
> > >
> > > Ok. I suppose any old platform like JUNO that missed this will have to
> > > update their DT to use the new scmi_perf_domain...well it should have
> > > anyway really, it is just that now it is silently failing.
> >
> > I don't think it's failing. The old binding for SCMI perf (using
> > clock-cells) is still supported the way they were before, which is
> > only for cpufreq.
> >
> > But, yes you are right, both the DT and the consumer driver would need
> > to be updated to support SCMI perf.
> >
>
> Not sure if you want to flag an error on platforms that doesn't use this.
> IMO probe succeeding doing nothing seems right. Won't returning the error
> from probe gets flagged as error during boot or module loading though
> it is harmless on the platform since it doesn't use it.
>
> > In fact, there is also one additional similar problem in probe, when
> > the number of perf-domains are zero. In that case, we should also
> > return an error code, rather than returning 0.
> >
> > >
> > > > In fact, there is also one additional similar problem in probe, when
> > > > the number of perf-domains are zero. In that case, we should also
> > > > return an error code, rather than returning 0.
> > > >
> > > > Would you mind updating the patch to cover both problems - or if you
> > > > are too busy, just let me know and I can help out.
> > >
> > > No problem, I can do it next week, but regarding the zero domain case,
> > > I remember I used to do the same on regulator/voltage driver and bail out
> > > when no domains were found, but we were asked by some customer to support
> > > instead the very useless and funny case of zero domains for some of their
> > > testing setup scenarios .. i.e. allowing the driver to load with zero domains
> > > (and do nothing) and then unload cleanly avoiding harms while unloading ...)
> > >
> > > Thoughts about this ? Can fix as you prefer .
> >
> > In my opinion, there is no point having a module/driver loaded to do
> > nothing. I would prefer to just return an error code.
> >
>
> IIRC we had this in one of the driver but there was a request to keep it
> this way as it is useful in SCMI f/w bringup/testing. Not all info/features
> need to be ready. That said I am fine if pmdomain prefers to flag 0 domains
> as error.

Well, I don't have a strong opinion around this particular case. My
opinion is more generic, keeping modules loaded wastes memory for no
good reason.

On the other hand, it may not be a problem in this case, as you suggested above.

Perhaps a consistent behaviour is better?

Kind regards
Uffe