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

[Baolu Lu]

On 2/20/25 18:15, Yunhui Cui wrote:
> 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;

If system interrupts are disabled here, locking is unnecessary. Hotplug
operations depend on interrupt events, so it's better to remove the
lock. The shutdown helper then appears like this:

void intel_iommu_shutdown(void)
{
        struct dmar_drhd_unit *drhd;
        struct intel_iommu *iommu = NULL;

        if (no_iommu || dmar_disabled)
                return;

        /*
         * System interrupts are disabled when it reaches here. Locking
         * is unnecessary when iterating the IOMMU list.
         */
        list_for_each_entry(drhd, &dmar_drhd_units, list) {
                if (drhd->ignored)
                        continue;

                iommu = drhd->iommu;
                /* Disable PMRs explicitly here. */
                iommu_disable_protect_mem_regions(iommu);
                iommu_disable_translation(iommu);
        }
}

Does it work for you?

Thanks,
baolu