nvmet: fix a possible leak when destroy a ctrl during qp establishment

In nvmet_sq_destroy we capture sq->ctrl early and if it is non-NULL we
know that a ctrl was allocated (in the admin connect request handler)
and we need to release pending AERs, clear ctrl->sqs and sq->ctrl
(for nvme-loop primarily), and drop the final reference on the ctrl.

However, a small window is possible where nvmet_sq_destroy starts (as
a result of the client giving up and disconnecting) concurrently with
the nvme admin connect cmd (which may be in an early stage). But *before*
kill_and_confirm of sq->ref (i.e. the admin connect managed to get an sq
live reference). In this case, sq->ctrl was allocated however after it was
captured in a local variable in nvmet_sq_destroy.
This prevented the final reference drop on the ctrl.

Solve this by re-capturing the sq->ctrl after all inflight request has
completed, where for sure sq->ctrl reference is final, and move forward
based on that.

This issue was observed in an environment with many hosts connecting
multiple ctrls simoutanuosly, creating a delay in allocating a ctrl
leading up to this race window.

Reported-by: Alex Turin <alex@vastdata.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index 2fde22323622e44366e6a194eb9af028799014e3..06f0c587f3437b8bdd57276a3929b91e2319e013 100644 (file)
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -818,6 +818,15 @@ void nvmet_sq_destroy(struct nvmet_sq *sq)
        percpu_ref_exit(&sq->ref);
        nvmet_auth_sq_free(sq);
 
+       /*
+        * we must reference the ctrl again after waiting for inflight IO
+        * to complete. Because admin connect may have sneaked in after we
+        * store sq->ctrl locally, but before we killed the percpu_ref. the
+        * admin connect allocates and assigns sq->ctrl, which now needs a
+        * final ref put, as this ctrl is going away.
+        */
+       ctrl = sq->ctrl;
+
        if (ctrl) {
                /*
                 * The teardown flow may take some time, and the host may not