5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sagi Grimberg <sagi@xxxxxxxxxxx>
[ Upstream commit c758b77d4a0a0ed3a1292b3fd7a2aeccd1a169a4 ]
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@xxxxxxxxxxxx>
Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/nvme/target/core.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index 2c44d5a95c8d6..ef2e500bccfdf 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -801,6 +801,15 @@ void nvmet_sq_destroy(struct nvmet_sq *sq)
wait_for_completion(&sq->free_done);
percpu_ref_exit(&sq->ref);
+ /*
+ * 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
--
2.43.0
