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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 SJ1PEPF00001CE0.mail.protection.outlook.com (10.167.242.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.339.3 via Frontend Transport; Tue, 18 Aug 2026 03:45:26 +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 15.2.2562.45; Mon, 17 Aug 2026 22:45:23 -0500 From: Shivank Garg Date: Tue, 18 Aug 2026 03:43:46 +0000 Subject: [PATCH v4 2/4] dmaengine: Fix device kref underflow in dma_chan_put() Precedence: bulk X-Mailing-List: linux-kernel@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: <20260818-dmaengine-kref-fix-v4-2-c6ef991462a0@amd.com> References: <20260818-dmaengine-kref-fix-v4-0-c6ef991462a0@amd.com> In-Reply-To: <20260818-dmaengine-kref-fix-v4-0-c6ef991462a0@amd.com> To: Vinod Koul , Frank Li , "Logan Gunthorpe" , Andrew Morton CC: , , , Shivank Garg , Frank Li X-Mailer: b4 0.15-dev-47d62 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787024717; l=1590; i=shivankg@amd.com; s=20260518; h=from:subject:message-id; bh=WyK1bhlIzw10xQpX3eRtqRomlgut0wJwNB8bjK+3rHk=; b=UpYw6uNXUfg6ea1Mtmu5CQCcTS2RTx12IM/nV2Khqjaj3aEujOGyz8i5jgeKC9mOQA/gLSbzm H7hJvqR/QqvB/cDJ2R57hpZcvN60ZHxW0XyJ+tVpliv3kePxdV0n30b X-Developer-Key: i=shivankg@amd.com; a=ed25519; pk=2l2QGTeXuGkZTtfmx0nPQU8iFZfjYmX/ymMojitevx4= X-ClientProxiedBy: satlexmb08.amd.com (10.181.42.217) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF00001CE0:EE_|PH8PR12MB7301:EE_ X-MS-Office365-Filtering-Correlation-Id: d8bee9b7-bd03-4154-851d-08defcdb242e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|376014|1800799024|82310400026|36860700016|18002099003|22082099003|56012099006|11063799006|10067099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(23010399003)(376014)(1800799024)(82310400026)(36860700016)(18002099003)(22082099003)(56012099006)(11063799006)(10067099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: QBfZvZXsX9ZPjxk9fWeoAv+gSoHmfTCZoOBb0TnMJKUZsktFKTXXs+Gtu9WNB3uHe5r3CUV1DIAnUfC7pZKSMPLTLlFTCsse5NsgyZZPdcn0+r/KUvqvhNh7vAicYwNQaK9kTCX7Sx53WrUIODgz1BIr554N9kk24C+taMMT+4fT2KtaWm7+fJzB7VegIDSwNL5CIljE0t/xGaAdGGsylUgPfz9gBdjp+hiBtn6EsLaM1f+Xu7ZtNq0sxv2pn24rIn63kv0Ix8/IYI13NBecQPr22yAFoBjv4ZTKJiIQlBBh+HZXUITSAbih/aV9SYDYU5GD5/HkfaNK3QKd+10QrAp6LL8knYqebSOFCT55pydqq7Pa+XYDrB7/sNfsPS02yVrS4JmDh+OqcXzfAWp3pIX5AdxIMxMhpOxvE0sxVmqPkPFt54oCc7A9AwZXVsT6 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Aug 2026 03:45:26.6847 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d8bee9b7-bd03-4154-851d-08defcdb242e 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: SJ1PEPF00001CE0.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR12MB7301 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; if (!dma_device_get(chan->device)) { // calls kref_get_unless_zero() 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") Reviewed-by: Frank Li 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 77638dc16e71..3ae53e11e54a 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -520,7 +520,9 @@ 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