[PATCH] nvme: fix deadlock between reset and scan
Sagi Grimberg
sagi at grimberg.me
Tue Nov 28 02:13:59 PST 2023
On 11/28/23 08:22, yaoma wrote:
> Hi Keith Busch
>
> Thanks for your reply.
>
> The idea to avoid such a deadlock between nvme_reset and nvme_scan is to
> ensure that no namespace can be added to ctrl->namespaces after
> nvme_start_freeze has already been called. We can achieve this goal by
> assessing the ctrl->state after we have already acquired the
> ctrl->namespaces_rwsem lock, to decide whether to add the namespace to
> the list or not.
> 1. After we determine that ctrl->state is LIVE, it may be immediately
> changed to another state. However, since we have already acquired the
> lock, other tasks cannot access ctrl->namespace, so we can still safely
> add the namespace to the list. After acquiring the lock,
> nvme_start_freeze will freeze all ns->q in the list, including any newly
> added namespaces.
> 2. Before the completion of nvme_reset, ctrl->state will not be changed
> to LIVE, so we will not add any more namespaces to the list. All ns->q
> in the list is frozen, so nvme_wait_freeze can exit normally.
I agree with the analysis, there is a hole between start_freeze and
freeze_wait that a scan may add a ns to the ctrl ns list.
However the fix should be to mark the ctrl with say NVME_CTRL_FROZEN
flag set in nvme_freeze_start and cleared in nvme_unfreeze (similar
to what we did with quiesce). Then the scan can check it before adding
the new namespace (under the namespaces_rwsem).
More information about the Linux-nvme
mailing list