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nvme: fix deadlock caused by ANA update wrong locking

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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 504db087aa) -> 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: 0d0b660f21 ("nvme: add ANA support")
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Sagi Grimberg 2020-04-02 09:34:54 -07:00 committed by Christoph Hellwig
parent a032e4f6d6
commit 657f1975e9
1 changed files with 2 additions and 2 deletions
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4
drivers/nvme/host/multipath.c
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@ -510,7 +510,7 @@ static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
if (!nr_nsids)
return 0;
down_write(&ctrl->namespaces_rwsem);
down_read(&ctrl->namespaces_rwsem);
list_for_each_entry(ns, &ctrl->namespaces, list) {
unsigned nsid = le32_to_cpu(desc->nsids[n]);
@ -521,7 +521,7 @@ static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
if (++n == nr_nsids)
break;
}
up_write(&ctrl->namespaces_rwsem);
up_read(&ctrl->namespaces_rwsem);
return 0;
}