[SRU][N:linux-azure-nvidia][PATCH 4/4] iommu/tegra241-cmdqv: do not use smp_processor_id in preemptible context

[John Cabaj]

From: "Luis Claudio R. Goncalves" <lgoncalv at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/2100199

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.

Cc: <stable at vger.kernel.org>
Fixes: 918eb5c856f6 ("iommu/arm-smmu-v3: Add in-kernel support for NVIDIA Tegra241 (Grace) CMDQV")
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv at redhat.com>
Reviewed-by: Jason Gunthorpe <jgg at nvidia.com>
Reviewed-by: Nicolin Chen <nicolinc at nvidia.com>
Tested-by: Nicolin Chen <nicolinc at nvidia.com>
Link: https://lore.kernel.org/r/Z1L1mja3nXzsJ0Pk@uudg.org
Signed-off-by: Will Deacon <will at kernel.org>
(cherry picked from commit 1f806218164d1bb93f3db21eaf61254b08acdf03)
Signed-off-by: John Cabaj <john.cabaj at canonical.com>
---
 drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
index 434114fde764..437140015e0c 100644
--- a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
+++ b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
@@ -338,7 +338,7 @@ 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;
-- 
2.43.0