Hi, On Tue, Sep 1, 2026 at 5:19 AM Zqiang <[email protected]> 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. >
I thought again about this and in my opinion this is not possible as it is already being handled by DEFINE_STATIC_SRCU() with a cleanup handling when the module is unloaded. I know that srcu subsystem does a lot of magic with modules init/exit functionality to call init_srcu_struct() and cleanup_srcu_struct(). See https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/module/main.c?h=v7.3-rc1#n2711 so this patch should be reverted. If they don't use a barrier there, the fix should be in the SRCU subsystem, but I believe the current SRCU implementation already handles this. - Alex > 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 <[email protected]> > --- > fs/dlm/lowcomms.c | 1 + > fs/dlm/midcomms.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c > index 2aff1c7c17de..ea8353c4638d 100644 > --- a/fs/dlm/lowcomms.c > +++ b/fs/dlm/lowcomms.c > @@ -1984,4 +1984,5 @@ void dlm_lowcomms_exit(void) > } > } > srcu_read_unlock(&connections_srcu, idx); > + srcu_barrier(&connections_srcu); > } > diff --git a/fs/dlm/midcomms.c b/fs/dlm/midcomms.c > index 8964164600d2..045431524494 100644 > --- a/fs/dlm/midcomms.c > +++ b/fs/dlm/midcomms.c > @@ -1178,6 +1178,7 @@ void dlm_midcomms_exit(void) > } > } > srcu_read_unlock(&nodes_srcu, idx); > + srcu_barrier(&nodes_srcu); > > dlm_lowcomms_exit(); > } > -- > 2.17.1 >
