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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 BY1PEPF0001AE1A.mail.protection.outlook.com (10.167.242.102) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.360.3 via Frontend Transport; Sat, 22 Aug 2026 19:22:20 +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; Sat, 22 Aug 2026 14:22:17 -0500 From: Shivank Garg Date: Sat, 22 Aug 2026 19:22:04 +0000 Subject: [PATCH v5 2/4] 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: <20260822-dmaengine-kref-fix-v5-2-d4a4ee47d927@amd.com> References: <20260822-dmaengine-kref-fix-v5-0-d4a4ee47d927@amd.com> In-Reply-To: <20260822-dmaengine-kref-fix-v5-0-d4a4ee47d927@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=1787426532; l=1642; i=shivankg@amd.com; s=20260518; h=from:subject:message-id; bh=UiUCtXvQIMfoyyI7A1JkRSEb8TYGQYCOz3ZIZD85bdM=; b=rNtsNNwQiQ9lRVAQ/8PtBe/+63Pj1K00qQJkPpSh3riSHmNfUfMePaARwwiCRpzf1sa7yaRbX AOJPItzCVELCs8jfSE1NVO8usJP2a2a5beomywb4YiSl1tczU8e1+KU X-Developer-Key: i=shivankg@amd.com; a=ed25519; pk=2l2QGTeXuGkZTtfmx0nPQU8iFZfjYmX/ymMojitevx4= X-ClientProxiedBy: satlexmb07.amd.com (10.181.42.216) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY1PEPF0001AE1A:EE_|SA1PR12MB7441:EE_ X-MS-Office365-Filtering-Correlation-Id: 49cd137a-66b8-4292-2098-08df0082b009 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|23010399003|376014|36860700016|1800799024|10067099003|56012099006|11063799006|22082099003|18002099003; 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)(82310400026)(23010399003)(376014)(36860700016)(1800799024)(10067099003)(56012099006)(11063799006)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: SKVjekDrADMoBB/FuSkcMIaTkZ0KwqaSP+lqttzR2Uf17kAJx2sZdFinylUn9Swajht2idB8dlIsmCDFcQV9u0X7vuuSt7pCEwcLJfFRG3BqtJdjs1/r4nkJ6wJ8j0FHxYkj7/YuST9cYQ+uTdjg3gDgZK49qq8uABgCsjjVckYE3FVBMFq73QHeRAMiANDxwSxtPafAZ/23djvTVAgK0wO6Wy4YSDuTsajjZWQE0868g+ZEKdft61cq/tkJOYPbUeog4jmffYKyulaU7Tr3OX8XxrNTzuJAhfgqXuUuu/1i2pgYbkJflVOxUsO8TjA9DI0Fi29DU1cgCrMgrhP0B7xRqJ9LEJuyckuUr1FO0HpL7r7xEmaFL1UAuwLIuuZTEdQxe9PsQgLBRXenSxpZzgo6tx6nb31I6GoPQvDJb15sbm6D3h+lwXDuxGTXhCbv X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Aug 2026 19:22:20.7776 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 49cd137a-66b8-4292-2098-08df0082b009 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: BY1PEPF0001AE1A.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB7441 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 Reviewed-by: Logan Gunthorpe 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 cb3b7bccce1f..f2760b039d93 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