| Message ID | Z1L1mja3nXzsJ0Pk@uudg.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] iommu/tegra241-cmdqv: do not use smp_processor_id in preemptible context | expand |
On Fri, Dec 06, 2024 at 10:01:14AM -0300, Luis Claudio R. Goncalves wrote: > During boot some of the calls to tegra241_cmdqv_get_cmdq() will happen > in preemptible context. As this function calls smp_processor_id(), if > CONFIG_DEBUG_PREEMPT is enabled, these calls will trigger a series of > "BUG: using smp_processor_id() in preemptible" backtraces. > > As tegra241_cmdqv_get_cmdq() only calls smp_processor_id() to use the > CPU number as a factor to balance out traffic on cmdq usage, it is safe > to use raw_smp_processor_id() here. > > v2: Sebastian helped identify that the problem was not exclusive to kernels > with PREEMPT_RT enabled. The delta between v1 and v2 is the description. > > Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com> > --- > drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Makes sense Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Jason
On Fri, Dec 06, 2024 at 10:01:14AM -0300, Luis Claudio R. Goncalves wrote: > During boot some of the calls to tegra241_cmdqv_get_cmdq() will happen > in preemptible context. As this function calls smp_processor_id(), if > CONFIG_DEBUG_PREEMPT is enabled, these calls will trigger a series of > "BUG: using smp_processor_id() in preemptible" backtraces. Confirmed the BUG prints. Should we CC stable tree? > As tegra241_cmdqv_get_cmdq() only calls smp_processor_id() to use the > CPU number as a factor to balance out traffic on cmdq usage, it is safe > to use raw_smp_processor_id() here. > > v2: Sebastian helped identify that the problem was not exclusive to kernels > with PREEMPT_RT enabled. The delta between v1 and v2 is the description. > > Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com> Tested-by: Nicolin Chen <nicolinc@nvidia.com> Thanks Nicolin
On Fri, 06 Dec 2024 10:01:14 -0300, Luis Claudio R. Goncalves wrote: > During boot some of the calls to tegra241_cmdqv_get_cmdq() will happen > in preemptible context. As this function calls smp_processor_id(), if > CONFIG_DEBUG_PREEMPT is enabled, these calls will trigger a series of > "BUG: using smp_processor_id() in preemptible" backtraces. > > As tegra241_cmdqv_get_cmdq() only calls smp_processor_id() to use the > CPU number as a factor to balance out traffic on cmdq usage, it is safe > to use raw_smp_processor_id() here. > > [...] Applied to will (for-joerg/arm-smmu/fixes), thanks! [1/1] iommu/tegra241-cmdqv: do not use smp_processor_id in preemptible context https://git.kernel.org/will/c/1f806218164d Cheers,
diff --git a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c index fcd13d301fff6..3ea4369e838fe 100644 --- a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c +++ b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c @@ -339,7 +339,7 @@ tegra241_cmdqv_get_cmdq(struct arm_smmu_device *smmu, * one CPU at a time can enter the process, while the others * will be spinning at the same lock. */ - lidx = smp_processor_id() % cmdqv->num_lvcmdqs_per_vintf; + lidx = raw_smp_processor_id() % cmdqv->num_lvcmdqs_per_vintf; vcmdq = vintf->lvcmdqs[lidx]; if (!vcmdq || !READ_ONCE(vcmdq->enabled)) return NULL;
During boot some of the calls to tegra241_cmdqv_get_cmdq() will happen in preemptible context. As this function calls smp_processor_id(), if CONFIG_DEBUG_PREEMPT is enabled, these calls will trigger a series of "BUG: using smp_processor_id() in preemptible" backtraces. As tegra241_cmdqv_get_cmdq() only calls smp_processor_id() to use the CPU number as a factor to balance out traffic on cmdq usage, it is safe to use raw_smp_processor_id() here. v2: Sebastian helped identify that the problem was not exclusive to kernels with PREEMPT_RT enabled. The delta between v1 and v2 is the description. Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com> --- drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)