b15eafb3f9
[ Upstream commit 657f1975e9d9c880fa13030e88ba6cc84964f1db ]
The deadlock combines 4 flows in parallel:
- ns scanning (triggered from reconnect)
- request timeout
- ANA update (triggered from reconnect)
- I/O coming into the mpath device
(1) ns scanning triggers disk revalidation -> update disk info ->
freeze queue -> but blocked, due to (2)
(2) timeout handler reference the g_usage_counter - > but blocks in
the transport .timeout() handler, due to (3)
(3) the transport timeout handler (indirectly) calls nvme_stop_queue() ->
which takes the (down_read) namespaces_rwsem - > but blocks, due to (4)
(4) ANA update takes the (down_write) namespaces_rwsem -> calls
nvme_mpath_set_live() -> which synchronize the ns_head srcu
(see commit 504db087aacc) -> but blocks, due to (5)
(5) I/O came into nvme_mpath_make_request -> took srcu_read_lock ->
direct_make_request > blk_queue_enter -> but blocked, due to (1)
==> the request queue is under freeze -> deadlock.
The fix is making ANA update take a read lock as the namespaces list
is not manipulated, it is just the ns and ns->head that are being
updated (which is protected with the ns->head lock).
Fixes:
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