Re: [PATCH] iommu/arm: Cleanup resources in case of probe error path

[Robin Murphy]

On 2021-07-01 10:01, Will Deacon wrote:
> On Thu, Jul 01, 2021 at 10:29:29AM +0200, Marek Szyprowski wrote:
> > Hi Robin,
> >
> > On 30.06.2021 16:01, Robin Murphy wrote:
> > > On 2021-06-30 14:48, Marek Szyprowski wrote:
> > > > On 30.06.2021 14:59, Will Deacon wrote:
> > > > > On Wed, Jun 30, 2021 at 02:48:15PM +0200, Marek Szyprowski wrote:
> > > > > > On 08.06.2021 18:45, Amey Narkhede wrote:
> > > > > > > If device registration fails, remove sysfs attribute
> > > > > > > and if setting bus callbacks fails, unregister the device
> > > > > > > and cleanup the sysfs attribute.
> > > > > > >
> > > > > > > Signed-off-by: Amey Narkhede <ameynarkhede03@xxxxxxxxx>
> > > > > > This patch landed in linux-next some time ago as commit 249c9dc6aa0d
> > > > > > ("iommu/arm: Cleanup resources in case of probe error path"). After
> > > > > > bisecting and some manual searching I finally found that it is
> > > > > > responsible for breaking s2idle on DragonBoard 410c. Here is the log
> > > > > > (captured with no_console_suspend):
> > > > > >
> > > > > > # time rtcwake -s10 -mmem
> > > > > > rtcwake: wakeup from "mem" using /dev/rtc0 at Thu Jan� 1 00:02:13 1970
> > > > > > PM: suspend entry (s2idle)
> > > > > > Filesystems sync: 0.002 seconds
> > > > > > Freezing user space processes ... (elapsed 0.006 seconds) done.
> > > > > > OOM killer disabled.
> > > > > > Freezing remaining freezable tasks ... (elapsed 0.004 seconds) done.
> > > > > > Unable to handle kernel NULL pointer dereference at virtual address
> > > > > > 0000000000000070
> > > > > > Mem abort info:
> > > > > > �� � ESR = 0x96000006
> > > > > > �� � EC = 0x25: DABT (current EL), IL = 32 bits
> > > > > > �� � SET = 0, FnV = 0
> > > > > > �� � EA = 0, S1PTW = 0
> > > > > > �� � FSC = 0x06: level 2 translation fault
> > > > > > Data abort info:
> > > > > > �� � ISV = 0, ISS = 0x00000006
> > > > > > �� � CM = 0, WnR = 0
> > > > > > user pgtable: 4k pages, 48-bit VAs, pgdp=000000008ad08000
> > > > > > [0000000000000070] pgd=0800000085c3c003, p4d=0800000085c3c003,
> > > > > > pud=0800000088dcf003, pmd=0000000000000000
> > > > > > Internal error: Oops: 96000006 [#1] PREEMPT SMP
> > > > > > Modules linked in: bluetooth ecdh_generic ecc rfkill ipv6 ax88796b
> > > > > > venus_enc venus_dec videobuf2_dma_contig asix crct10dif_ce adv7511
> > > > > > snd_soc_msm8916_analog qcom_spmi_temp_alarm rtc_pm8xxx qcom_pon
> > > > > > qcom_camss qcom_spmi_vadc videobuf2_dma_sg qcom_vadc_common msm
> > > > > > venus_core v4l2_fwnode v4l2_async snd_soc_msm8916_digital
> > > > > > videobuf2_memops snd_soc_lpass_apq8016 snd_soc_lpass_cpu v4l2_mem2mem
> > > > > > snd_soc_lpass_platform snd_soc_apq8016_sbc videobuf2_v4l2
> > > > > > snd_soc_qcom_common qcom_rng videobuf2_common i2c_qcom_cci
> > > > > > qnoc_msm8916
> > > > > > videodev mc icc_smd_rpm mdt_loader socinfo display_connector rmtfs_mem
> > > > > > CPU: 1 PID: 1522 Comm: rtcwake Not tainted 5.13.0-next-20210629 #3592
> > > > > > Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
> > > > > > pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
> > > > > > pc : msm_runtime_suspend+0x1c/0x60 [msm]
> > > > > > lr : msm_pm_suspend+0x18/0x38 [msm]
> > > > > > ...
> > > > > > Call trace:
> > > > > > �� �msm_runtime_suspend+0x1c/0x60 [msm]
> > > > > > �� �msm_pm_suspend+0x18/0x38 [msm]
> > > > > > �� �dpm_run_callback+0x84/0x378
> > > > > I wonder if we're missing a pm_runtime_disable() call on the failure
> > > > > path?
> > > > > i.e. something like the diff below...
> > > >
> > > > I've checked and it doesn't fix anything.
> > >
> > > What's happened previously? Has an IOMMU actually failed to probe, or
> > > is this a fiddly "code movement unveils latent bug elsewhere" kind of
> > > thing? There doesn't look to be much capable of going wrong in
> > > msm_runtime_suspend() itself, so is the DRM driver also in a broken
> > > half-probed state where it's left its pm_runtime_ops behind without
> > > its drvdata being valid?
> > I finally had some time to analyze this issue. It turned out that with
> > this patch, iommu fails to probe for soc:iommu@1f08000 device, while it
> > worked fine before. This happens because this patch adds a check for the
> > return value of the bus_set_iommu() in
> > drivers/iommu/arm/arm-smmu/qcom_iommu.c. When I removed that check, it
> > probes successfully again. It looks that there are already iommu ops
> > registered for platform bus, before qcom_iommu probes. On the other
> > hand, if I remember correctly they are not used during the device
> > registration, but they are needed for some legacy stuff. I can send a
> > patch restoring old code flow if you think that this is a right solution.
>
> Yes, let's just revert the qcom_iommu.c changes from that patch for now.
> The pm runtime stuff looks dodgy anyway so I think this needs more thought.

Oh, right, blindly returning the -EBUSY from bus_set_iommu() because 
we're not the first instance to probe is definitely the wrong thing to 
do as well. It's still not clear why failing makes the DRM driver fall 
over, but +1 to qcom-iommu needing some deeper consideration.

Robin.