[PATCH] iommu/vt-d: fix system hang on reboot -f

[Yunhui Cui]

When entering intel_iommu_shutdown, system interrupts are disabled,
and the reboot process might be scheduled out by down_write(). If the
scheduled process does not yield (e.g., while(1)), the system will hang.

Signed-off-by: Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx>
---
 drivers/iommu/intel/iommu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index cc46098f875b..76a1d83b46bf 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2871,7 +2871,8 @@ void intel_iommu_shutdown(void)
 	if (no_iommu || dmar_disabled)
 		return;
 
-	down_write(&dmar_global_lock);
+	if (!down_write_trylock(&dmar_global_lock))
+		return;
 
 	/* Disable PMRs explicitly here. */
 	for_each_iommu(iommu, drhd)
-- 
2.39.2