Re: [PATCH] dlm: wait for outstanding SRCU callbacks to complete in exit paths

[Alexander Aring]

Hi,

On Tue, Sep 1, 2026 at 5:19 AM Zqiang <qiang.zhang@xxxxxxxxx> wrote:
>
> The dlm_lowcomms_exit() and dlm_midcomms_exit() iterate over the
> srcu protected connection and node hash tables and hand each
> element to call_srcu() for deferred freeing (connection_release()
> and midcomms_node_release()). call_srcu() is asynchronous: the
> callbacks are invoked only after an SRCU grace period, which may
> happen after the exit function has already returned.
>
> These exit functions are reached from exit_dlm() on module unload.
> Once they return, module teardown continues and the module text
> may be unloaded while call_srcu() callbacks are still pending. When
> such a callback finally runs, it executes freed module code and
> touches the static SRCU domains that are being torn down, resulting
> in a use-after-free.
>
> Add an srcu_barrier() after the call_srcu() loop in each exit function
> to wait for all outstanding callbacks of the respective SRCU domain to
> complete before returning. In dlm_midcomms_exit() the barrier is issued
> before dlm_lowcomms_exit() so that node callbacks are drained prior to
> tearing down the lower layer.
>
> Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxx>

Acked-by: Alexander Aring <aahringo@xxxxxxxxxx>

- Alex