linux-kernel - [PATCH] dmaengine: fix locking for dma_channel

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Date:   Tue, 22 Feb 2022 03:58:49 +0200
From:   Dāvis Mosāns <davispuh@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Vinod Koul <vkoul@...nel.org>, dmaengine@...r.kernel.org,
        Dāvis Mosāns <davispuh@...il.com>
Subject: [PATCH] dmaengine: fix locking for dma_channel_rebalance

dma_channel_rebalance comment says:
>  Must be called under dma_list_mutex

We have few places where it wasn't done and could cause crashes.
So invoke it only when it's under mutex.
---
 drivers/dma/dmaengine.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 2cfa8458b51be..5198bdf7ee804 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -1098,7 +1098,10 @@ int dma_async_device_channel_register(struct dma_device *device,
 	if (rc < 0)
 		return rc;
 
+	mutex_lock(&dma_list_mutex);
 	dma_channel_rebalance();
+	mutex_unlock(&dma_list_mutex);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(dma_async_device_channel_register);
@@ -1124,7 +1127,9 @@ void dma_async_device_channel_unregister(struct dma_device *device,
 					 struct dma_chan *chan)
 {
 	__dma_async_device_channel_unregister(device, chan);
+	mutex_lock(&dma_list_mutex);
 	dma_channel_rebalance();
+	mutex_unlock(&dma_list_mutex);
 }
 EXPORT_SYMBOL_GPL(dma_async_device_channel_unregister);
 
-- 
2.35.1