Hi, On Wed, Sep 2, 2026 at 10:49 AM Zqiang <[email protected]> wrote: > > > > > Hi, > > > > On Wed, Sep 2, 2026 at 10:30 AM Zqiang <[email protected]> wrote: > > > > > > > > > > > > > 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 should rephrase it: > > > > > > Due to missed call to the srcu_barrier(), when invoke > > > cleanup_srcu_struct() > > > > > Then there need to be a MUST call of srcu_barrier() before > > cleanup_srcu_struct() every time. > > If there are some call_srcu() call, the srcu_barrier() should be called > before cleanup_srcu_struct(). > usually, when the cleanup_srcu_struct() run, we should ensure that there are > no pending SRCU callbacks > or ongoing SRCU grace periods at this time. >
For me, this is a MUST because who is maintaining something to know if it was ever called? > there are another reason: > > The midcomms_node_release() srcu callback can call call_rcu(), we must wait > the all > call_rcu() to complete, because rcu_barrier() which in dlm_memory_exit() is > required > to successfully intercept these RCU callbacks. > Yes, I can see why "nodes_srcu" is necessary as this has something to do with kmem_cache is being involed. The "connections_srcu" is necessary for the above reason that the srcu API requires you to call srcu_barrier() before cleanup_srcu_struct() because for whatever reason we don't do that in cleanup_srcu_struct() as I understand it now. - Alex
