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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Michal Hocko <mhocko@suse.com>,
        David Hildenbrand <david@redhat.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Scott Cheloha <cheloha@linux.vnet.ibm.com>,
        Nathan Lynch <nathanl@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.17 507/772] drivers/base/memory: fix an unlikely reference counting issue in __add_memory_block()
Date:   Tue,  7 Jun 2022 19:01:39 +0200
Message-Id: <20220607165003.919479616@linuxfoundation.org>
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From: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

[ Upstream commit f47f758cff59c68015d6b9b9c077110df7c2c828 ]

__add_memory_block() calls both put_device() and device_unregister() when
storing the memory block into the xarray.  This is incorrect because
xarray doesn't take an additional reference and device_unregister()
already calls put_device().

Triggering the issue looks really unlikely and its only effect should be
to log a spurious warning about a ref counted issue.

Link: https://lkml.kernel.org/r/d44c63d78affe844f020dc02ad6af29abc448fc4.1650611702.git.christophe.jaillet@wanadoo.fr
Fixes: 4fb6eabf1037 ("drivers/base/memory.c: cache memory blocks in xarray to accelerate lookup")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Scott Cheloha <cheloha@linux.vnet.ibm.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/base/memory.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 60c38f9cf1a7..c0d501a3a714 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -634,10 +634,9 @@ int register_memory(struct memory_block *memory)
 	}
 	ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
 			      GFP_KERNEL));
-	if (ret) {
-		put_device(&memory->dev);
+	if (ret)
 		device_unregister(&memory->dev);
-	}
+
 	return ret;
 }
 
-- 
2.35.1