forked from Minki/linux
819f7b88b4
In function nvmet_async_event_process() we only process AENs iff
there is an open slot on the ctrl->async_event_cmds[] && aen
event list posted by the target is not empty. This keeps host
posted AEN outstanding if target generated AEN list is empty.
We do cleanup the target generated entries from the aen list in
nvmet_ctrl_free()-> nvmet_async_events_free() but we don't
process AEN posted by the host. This leads to following problem :-
When processing admin sq at the time of nvmet_sq_destroy() holds
an extra percpu reference(atomic value = 1), so in the following code
path after switching to atomic rcu, release function (nvmet_sq_free())
is not getting called which blocks the sq->free_done in
nvmet_sq_destroy() :-
nvmet_sq_destroy()
percpu_ref_kill_and_confirm()
- __percpu_ref_switch_mode()
-- __percpu_ref_switch_to_atomic()
--- call_rcu() -> percpu_ref_switch_to_atomic_rcu()
---- /* calls switch callback */
- percpu_ref_put()
-- percpu_ref_put_many(ref, 1)
--- else if (unlikely(atomic_long_sub_and_test(nr, &ref->count)))
---- ref->release(ref); <---- Not called.
This results in indefinite hang:-
void nvmet_sq_destroy(struct nvmet_sq *sq)
...
if (ctrl && ctrl->sqs && ctrl->sqs[0] == sq) {
nvmet_async_events_process(ctrl, status);
percpu_ref_put(&sq->ref);
}
percpu_ref_kill_and_confirm(&sq->ref, nvmet_confirm_sq);
wait_for_completion(&sq->confirm_done);
wait_for_completion(&sq->free_done); <-- Hang here
Which breaks the further disconnect sequence. This problem seems to be
introduced after commit
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