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client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by CH1PEPF0000AD74.mail.protection.outlook.com (10.167.244.52) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.71.7 via Frontend Transport; Tue, 26 May 2026 11:19:35 +0000 Received: from [127.0.1.1] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.41; Tue, 26 May 2026 06:19:33 -0500 From: Shivank Garg Date: Tue, 26 May 2026 11:19:18 +0000 Subject: [PATCH v2 1/2] dmaengine: Fix device kref underflow in dma_chan_put() Precedence: bulk X-Mailing-List: dmaengine@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-ID: <20260526-dmaengine-kref-fix-v2-1-3df60afac01d@amd.com> References: <20260526-dmaengine-kref-fix-v2-0-3df60afac01d@amd.com> In-Reply-To: <20260526-dmaengine-kref-fix-v2-0-3df60afac01d@amd.com> To: Vinod Koul , Frank Li , "Logan Gunthorpe" CC: , , , Shivank Garg X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: fYyZjvk8qmO/NYtynmenOl5xR4782Cr12Q3Xb/Vp39u4kIZfp4kBXSKC2t6Srx4axhF5C9yRMd5bcoiO1kSq852a1xJkYfg74io7i3V84zbeq72STjEyyDj1WkcaLlKeW/LDMXvsbMQI3DrU1Ymua0HTZnfG2xF7qdO2KzhN0014j9xwjVQg7NfB6gbv4fU0hVc3T8JXx4djGzsVvTcb9KwgVHS/tcaqX3j6t/AYLLX/H67LBzYBN8YxFcO4loGvGlrVZHlyjp6Hc67tpStz5sFv1tDG1pFMdWS6Hmmp530xDQs1hy8Ef3Do831/BZMJv+pq0iICYrG2BaGVbuvuKPnA/XrErJj4NumeSNXVE7yVe2/8Of0jmtnmHYR6M62xTJLBvEfOv1ksl1a39MokFFi6B1AV0qg+bDHVxh9gQDXpM7Yc2HYuqSpqYDlRvsTk X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 May 2026 11:19:35.7962 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 07711ca2-f96c-4230-1262-08debb18ab2b X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CH1PEPF0000AD74.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB9253 dma_chan_get() takes chan->device->ref only on the slow path: /* no kref on fast path */ if (chan->client_count) { __module_get(owner); chan->client_count++; return 0; } if (!try_module_get(owner)) return -ENODEV; ret = kref_get_unless_zero(&chan->device->ref); dma_chan_put() drops the ref unconditionally, so every fast-path get/put pair drops one extra device reference. The bug fires when two conditions hold together: a non-private provider has a persistent client holding chan->client_count > 0 and another client cycles dmaengine_get()/dmaengine_put(). When the kref hits zero, the subsequent dma_find_channel() returns NULL even though the provider module is still loaded. Fix this by dropping device->ref only on the last put, matching the single slow-path get. Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct") Signed-off-by: Shivank Garg --- drivers/dma/dmaengine.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 405bd2fbb4a3b94fd0bf44526f656f6a19feaad0..605bfa477a004cc0b03957ffb85a52308f903441 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -515,7 +515,9 @@ static void dma_chan_put(struct dma_chan *chan) chan->route_data = NULL; } - dma_device_put(chan->device); + /* This channel is not in use anymore, drop the device ref */ + if (!chan->client_count) + dma_device_put(chan->device); module_put(dma_chan_to_owner(chan)); } -- 2.43.0