On Wed, Jan 21, 2026 at 10:12 PM Danilo Krummrich wrote: > > Commit 0b4eeee2876f ("iommu/arm-smmu-qcom: Register the TBU driver in > qcom_smmu_impl_init") intended to also probe the TBU driver when > CONFIG_ARM_SMMU_QCOM_DEBUG is disabled, but also moved the corresponding > platform_driver_register() call into qcom_smmu_impl_init() which is > called from arm_smmu_device_probe(). > > However, it neither makes sense to register drivers from probe() > callbacks of other drivers, nor does the driver core allow registering > drivers with a device lock already being held. > > The latter was revealed by commit dc23806a7c47 ("driver core: enforce > device_lock for driver_match_device()") leading to a deadlock condition > described in [1]. > > Additionally, it was noted by Robin that the current approach is > potentially racy with async probe [2]. > > Hence, fix this by registering the qcom_smmu_tbu_driver from > module_init(). Unfortunately, due to the vendoring of the driver, this > requires an indirection through arm-smmu-impl.c. > > Reported-by: Mark Brown > Closes: https://lore.kernel.org/lkml/7ae38e31-ef31-43ad-9106-7c76ea0e8596@sirena.org.uk/ > Link: https://lore.kernel.org/lkml/DFU7CEPUSG9A.1KKGVW4HIPMSH@kernel.org/ [1] > Link: https://lore.kernel.org/lkml/0c0d3707-9ea5-44f9-88a1-a65c62e3df8d@arm.com/ [2] > Fixes: dc23806a7c47 ("driver core: enforce device_lock for driver_match_device()") > Fixes: 0b4eeee2876f ("iommu/arm-smmu-qcom: Register the TBU driver in qcom_smmu_impl_init") Glad the backtrace helped identify the root cause. I applied this patch to the qemu setup where I successfully reproduced the boot hang earlier, and the deadlock is resolved. Tested-by: Wang Jiayue Reviewed-by: Wang Jiayue > Signed-off-by: Danilo Krummrich > --- > drivers/iommu/arm/arm-smmu/arm-smmu-impl.c | 14 +++++++++++++ > drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 14 +++++++++---- > drivers/iommu/arm/arm-smmu/arm-smmu.c | 24 +++++++++++++++++++++- > drivers/iommu/arm/arm-smmu/arm-smmu.h | 5 +++++ > 4 files changed, 52 insertions(+), 5 deletions(-) > > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c > index db9b9a8e139c..4565a58bb213 100644 > --- a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c > @@ -228,3 +228,17 @@ struct arm_smmu_device *arm_smmu_impl_init(struct arm_smmu_device *smmu) > > return smmu; > } > + > +int __init arm_smmu_impl_module_init(void) > +{ > + if (IS_ENABLED(CONFIG_ARM_SMMU_QCOM)) > + return qcom_smmu_module_init(); > + > + return 0; > +} > + > +void __exit arm_smmu_impl_module_exit(void) > +{ > + if (IS_ENABLED(CONFIG_ARM_SMMU_QCOM)) > + qcom_smmu_module_exit(); > +} > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c > index 573085349df3..22906d2c9a2d 100644 > --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c > @@ -774,10 +774,6 @@ struct arm_smmu_device *qcom_smmu_impl_init(struct arm_smmu_device *smmu) > { > const struct device_node *np = smmu->dev->of_node; > const struct of_device_id *match; > - static u8 tbu_registered; > - > - if (!tbu_registered++) > - platform_driver_register(&qcom_smmu_tbu_driver); > > #ifdef CONFIG_ACPI > if (np == NULL) { > @@ -802,3 +798,13 @@ struct arm_smmu_device *qcom_smmu_impl_init(struct arm_smmu_device *smmu) > > return smmu; > } > + > +int __init qcom_smmu_module_init(void) > +{ > + return platform_driver_register(&qcom_smmu_tbu_driver); > +} > + > +void __exit qcom_smmu_module_exit(void) > +{ > + platform_driver_unregister(&qcom_smmu_tbu_driver); > +} > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c > index 5e690cf85ec9..1e218fbea35a 100644 > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c > @@ -2365,7 +2365,29 @@ static struct platform_driver arm_smmu_driver = { > .remove = arm_smmu_device_remove, > .shutdown = arm_smmu_device_shutdown, > }; > -module_platform_driver(arm_smmu_driver); > + > +static int __init arm_smmu_init(void) > +{ > + int ret; > + > + ret = platform_driver_register(&arm_smmu_driver); > + if (ret) > + return ret; > + > + ret = arm_smmu_impl_module_init(); > + if (ret) > + platform_driver_unregister(&arm_smmu_driver); > + > + return ret; > +} > +module_init(arm_smmu_init); > + > +static void __exit arm_smmu_exit(void) > +{ > + arm_smmu_impl_module_exit(); > + platform_driver_unregister(&arm_smmu_driver); > +} > +module_exit(arm_smmu_exit); > > MODULE_DESCRIPTION("IOMMU API for ARM architected SMMU implementations"); > MODULE_AUTHOR("Will Deacon "); > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h > index 2dbf3243b5ad..26d2e33cd328 100644 > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h > @@ -540,6 +540,11 @@ struct arm_smmu_device *arm_smmu_impl_init(struct arm_smmu_device *smmu); > struct arm_smmu_device *nvidia_smmu_impl_init(struct arm_smmu_device *smmu); > struct arm_smmu_device *qcom_smmu_impl_init(struct arm_smmu_device *smmu); > > +int __init arm_smmu_impl_module_init(void); > +void __exit arm_smmu_impl_module_exit(void); > +int __init qcom_smmu_module_init(void); > +void __exit qcom_smmu_module_exit(void); > + > void arm_smmu_write_context_bank(struct arm_smmu_device *smmu, int idx); > int arm_mmu500_reset(struct arm_smmu_device *smmu); > > > base-commit: dc23806a7c47ec5f1293aba407fb69519f976ee0 > -- > 2.52.0 >