linux-kernel - [PATCH AUTOSEL 5.2 56/76] nvme-multipath: fix possible I/O hang when paths are updated

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Message-Id: <20190829181311.7562-56-sashal@kernel.org>
Date:   Thu, 29 Aug 2019 14:12:51 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Anton Eidelman <anton@...htbitslabs.com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>, Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <sashal@...nel.org>, linux-nvme@...ts.infradead.org
Subject: [PATCH AUTOSEL 5.2 56/76] nvme-multipath: fix possible I/O hang when paths are updated

From: Anton Eidelman <anton@...htbitslabs.com>

[ Upstream commit 504db087aaccdb32af61539916409f7dca31ceb5 ]

nvme_state_set_live() making a path available triggers requeue_work
in order to resubmit requests that ended up on requeue_list when no
paths were available.

This requeue_work may race with concurrent nvme_ns_head_make_request()
that do not observe the live path yet.
Such concurrent requests may by made by either:
- New IO submission.
- Requeue_work triggered by nvme_failover_req() or another ana_work.

A race may cause requeue_work capture the state of requeue_list before
more requests get onto the list. These requests will stay on the list
forever unless requeue_work is triggered again.

In order to prevent such race, nvme_state_set_live() should
synchronize_srcu(&head->srcu) before triggering the requeue_work and
prevent nvme_ns_head_make_request referencing an old snapshot of the
path list.

Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Anton Eidelman <anton@...htbitslabs.com>
Signed-off-by: Sagi Grimberg <sagi@...mberg.me>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/nvme/host/multipath.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index e942b3e840687..4f599366bc5ae 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -356,6 +356,7 @@ static void nvme_mpath_set_live(struct nvme_ns *ns)
 		srcu_read_unlock(&head->srcu, srcu_idx);
 	}
 
+	synchronize_srcu(&ns->head->srcu);
 	kblockd_schedule_work(&ns->head->requeue_work);
 }
 
-- 
2.20.1