On 2021-12-10 18:04, John Garry via iommu wrote:
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" :)
Weird... the original patch file here and the copy received by lore via
linux-iommu look fine, gremlins in your MUA or delivery path perhaps?
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>
Thanks John!
Robin.
