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

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Message-ID: <622aa790-6560-4be9-bfb4-736809a249bc@linux.intel.com>
Date: Mon, 24 Feb 2025 09:02:47 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Yunhui Cui <cuiyunhui@...edance.com>, dwmw2@...radead.org,
 joro@...tes.org, will@...nel.org, robin.murphy@....com,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: fix system hang on reboot -f

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@...edance.com>
> ---
>   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