From: Sagi Grimberg <sagi@grimberg.me>
To: linux-nvme@lists.infradead.org, Keith Busch <kbusch@kernel.org>,
Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Subject: [PATCH] nvme: fix deadlock caused by ana update wrong locking
Date: Thu, 2 Apr 2020 09:18:13 -0700 [thread overview]
Message-ID: <20200402161813.16244-1-sagi@grimberg.me> (raw)
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 (which is protected
with the ns->head lock.
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
---
drivers/nvme/host/multipath.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 61bf87592570..54603bd3e02d 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -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;
}
--
2.20.1
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next reply other threads:[~2020-04-02 16:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-02 16:18 Sagi Grimberg [this message]
2020-04-02 16:31 ` [PATCH] nvme: fix deadlock caused by ana update wrong locking Keith Busch
2020-04-03 6:13 ` Hannes Reinecke
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