Re: [PATCH v2 01/11] iommu/iova: Fix race between FQ timeout and teardown

[John Garry]

On 10/12/2021 17:54, Robin Murphy wrote:
> From: Xiongfeng Wang<wangxiongfeng2@xxxxxxxxxx>
>
> It turns out to be possible for hotplugging out a device to reach the
> stage of tearing down the device's group and default domain before the
> domain's flush queue has drained naturally. At this point, it is then
> possible for the timeout to expire just*before*  the del_timer() call

super nit: "just*before*  the" - needs a whitespace before "before" :)

> from free_iova_flush_queue(), such that we then proceed to free the FQ
> resources while fq_flush_timeout() is still accessing them on another
> CPU. Crashes due to this have been observed in the wild while removing
> NVMe devices.
>
> Close the race window by using del_timer_sync() to safely wait for any
> active timeout handler to finish before we start to free things. We
> already avoid any locking in free_iova_flush_queue() since the FQ is
> supposed to be inactive anyway, so the potential deadlock scenario does
> not apply.
>
> Fixes: 9a005a800ae8 ("iommu/iova: Add flush timer")
> Signed-off-by: Xiongfeng Wang<wangxiongfeng2@xxxxxxxxxx>
> [ rm: rewrite commit message ]
> Signed-off-by: Robin Murphy<robin.murphy@xxxxxxx>

FWIW,

Reviewed-by: John Garry <john.garry@xxxxxxxxxx>