linux-kernel - [PATCH v2 2/5] dmaengine: Call module_put() after device_free_chan

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Date:   Mon,  9 Dec 2019 17:24:34 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
        Vinod Koul <vkoul@...nel.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Kit Chow <kchow@...aio.com>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: [PATCH v2 2/5] dmaengine: Call module_put() after device_free_chan_resources()

The module reference is taken to ensure the callbacks still exist
when they are called. If the channel holds the last reference to the
module, the module can disappear before device_free_chan_resources() is
called and would cause a call into free'd memory.

Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
---
 drivers/dma/dmaengine.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 4b604086b1b3..776fdf535a3a 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -250,7 +250,6 @@ static void dma_chan_put(struct dma_chan *chan)
 		return;
 
 	chan->client_count--;
-	module_put(dma_chan_to_owner(chan));
 
 	/* This channel is not in use anymore, free it */
 	if (!chan->client_count && chan->device->device_free_chan_resources) {
@@ -259,6 +258,8 @@ static void dma_chan_put(struct dma_chan *chan)
 		chan->device->device_free_chan_resources(chan);
 	}
 
+	module_put(dma_chan_to_owner(chan));
+
 	/* If the channel is used via a DMA request router, free the mapping */
 	if (chan->router && chan->router->route_free) {
 		chan->router->route_free(chan->router->dev, chan->route_data);
-- 
2.20.1