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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, Laurent Fert <laurent.fert@intel.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.4 062/131] stm class: Fix unlocking braino in the error path
Date:   Mon,  1 Apr 2019 19:02:12 +0200
Message-Id: <20190401170057.457540125@linuxfoundation.org>
In-Reply-To: <20190401170051.645954551@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

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

[ Upstream commit 1810f2c44817c74ca3d05d1e3981e3a2e2ceb6f5 ]

If an illegal attempt is made to unlink stm source device from an
stm device, the stm device's link spinlock mistakenly remains locked.
While this really shouldn't happen (there's a warning in place), the
locking should remain in order so that we can still recover from this
situation if it indeed does happen.

This patch unifies the unlocking in the exit path of
__stm_source_link_drop() to fix this.

Reported-by: Laurent Fert <laurent.fert@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/hwtracing/stm/core.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index e4fa583b57a6..d4deac108578 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -817,10 +817,8 @@ static void __stm_source_link_drop(struct stm_source_device *src,
 	spin_lock(&stm->link_lock);
 	spin_lock(&src->link_lock);
 	link = srcu_dereference_check(src->link, &stm_source_srcu, 1);
-	if (WARN_ON_ONCE(link != stm)) {
-		spin_unlock(&src->link_lock);
-		return;
-	}
+	if (WARN_ON_ONCE(link != stm))
+		goto unlock;
 
 	stm_output_free(link, &src->output);
 	list_del_init(&src->link_entry);
@@ -828,6 +826,7 @@ static void __stm_source_link_drop(struct stm_source_device *src,
 	stm_put_device(link);
 	rcu_assign_pointer(src->link, NULL);
 
+unlock:
 	spin_unlock(&src->link_lock);
 	spin_unlock(&stm->link_lock);
 }
-- 
2.19.1