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

[yunhui cui]

Hi Ethan,

On Fri, Feb 21, 2025 at 4:40 PM Ethan Zhao <haifeng.zhao@xxxxxxxxxxxxxxx> wrote:
>
>
> 在 2025/2/20 18:15, Yunhui Cui 写道:
> > When entering intel_iommu_shutdown, system interrupts are disabled,
>
> System interrupts were disabled ? you mean all interrupts were disabled
> when entering intel_iommu_shutdown(), perhaps it is not true, at least
> for upstream latest code.
>
> > 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.
>
> No NMI lockup watchdog jumping out here ?

Steps to reproduce:

1. Avoid return in:
if (no_iommu || dmar_disabled)
    return;

2. Write a.out with while(1).

3. ./a.out &; reboot -f.

4. Observe. Send NMI via BIOS to check system response.

5. Add console=ttyS0,115200 to cmdline to increase reproduction chance.

Let's continue discussing based on the above.

>
> Thanks,
> Ethan
>
> >
> > 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)
>
> --
> "firm, enduring, strong, and long-lived"
>

Thanks,
Yunhui