linux-kernel - [PATCH 4.14 120/178] nvme: use kref_get_unless_zero in nvme_find_get

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Date:   Mon, 18 Dec 2017 16:49:16 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Hannes Reinecke <hare@...e.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.14 120/178] nvme: use kref_get_unless_zero in nvme_find_get_ns

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christoph Hellwig <hch@....de>


[ Upstream commit 2dd4122854f697afc777582d18548dded03ce5dd ]

For kref_get_unless_zero to protect against lookup vs free races we need
to use it in all places where we aren't guaranteed to already hold a
reference.  There is no such guarantee in nvme_find_get_ns, so switch to
kref_get_unless_zero in this function.

Signed-off-by: Christoph Hellwig <hch@....de>
Reviewed-by: Sagi Grimberg <sagi@...mberg.me>
Reviewed-by: Hannes Reinecke <hare@...e.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/nvme/host/core.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2299,7 +2299,8 @@ static struct nvme_ns *nvme_find_get_ns(
 	mutex_lock(&ctrl->namespaces_mutex);
 	list_for_each_entry(ns, &ctrl->namespaces, list) {
 		if (ns->ns_id == nsid) {
-			kref_get(&ns->kref);
+			if (!kref_get_unless_zero(&ns->kref))
+				continue;
 			ret = ns;
 			break;
 		}