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To: Jihan LIN , CC: , , , , , , , , , , , , , , , , , References: <20260917043339.2093426-8-suleiman@google.com> <887eff66-35f3-4703-8ff7-c0c959621b69@gmail.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <887eff66-35f3-4703-8ff7-c0c959621b69@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY1PEPF000264B0:EE_|CY3PR12MB9631:EE_ X-MS-Office365-Filtering-Correlation-Id: b36ee8e9-6d99-426d-2962-08df14c98285 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|7416014|376014|36860700016|82310400026|13003099007|10067099003|4143699003|11063799006|56012099006|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)(1800799024)(23010399003)(7416014)(376014)(36860700016)(82310400026)(13003099007)(10067099003)(4143699003)(11063799006)(56012099006)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: D6CnNZG4A5ljqyp8EX6N76LmtLmC2FrTx1n3WlybtuGWFT0GlxWzNeBwa5q6lAhiMwEpBwFrswhF66OoJpJjDjC8r+cXpJcj/QrBAhOS24iKVQeDSINrGhql+a55YIAkcUB5zYFhXDyIX+0MwvNfsBX9jnodoLtywnkHkeFck2D5F/etl2HbIWmaJPQABXB4kA/ttplhyw4fIISDeG7AmXgivMAoX3HAleEwyp7egJMyRC6BmB++FZM7O5YpPZeyu/gFQSl/ZFpKEw9OEK9yYatm3UkS12YSD2sdfRiuP5s++KrShBTi+XNYFpwBoKyrENclcH0LljW/uT6gVgot03dZuYl0eYqG8VKR0/683+qFw8VWNVISRLsLqLnKdJvnkpzEIYCxCcpD4EYjGVgaUWvcSLVIKrz8JBVptJQi/GK1DgnCqjG+KI5+Q9vCEE8q X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Sep 2026 14:39:41.9625 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b36ee8e9-6d99-426d-2962-08df14c98285 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: BY1PEPF000264B0.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY3PR12MB9631 On 9/17/2026 6:48 PM, Jihan LIN wrote: > [You don't often get email from linjh22s@gmail.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] > > Hi Suleiman, > > Thanks for your RFC series. > >> diff --git a/kernel/futex/ping.c b/kernel/futex/ping.c >> index ebcd3c4a7793..689f149f7150 100644 >> --- a/kernel/futex/ping.c >> +++ b/kernel/futex/ping.c >> @@ -370,6 +370,9 @@ int futex_lock_ping(u32 __user *uaddr, unsigned int flags, ktime_t *time, >> >> queued = false; >> while (1) { >> + set_task_blocked_on(current, &q.ping_state->ping_mutex, >> + BO_T_PING_FUTEX); >> + >> set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE); >> if (!queued) { >> > > A userspace deadlock seems to turn into a kernel lockup. > Consider threads A and B on CPU0, unlocked PING futexes F1 and F2, with > the following ordering: > > A: CAS(F1, gettid(A)) > B: CAS(F2, gettid(B)) > A: futex(&F2, FUTEX_LOCK_PING) <-- T1 > B: futex(&F1, FUTEX_LOCK_PING) <-- T2 > > Since futex_lock_ping_atomic() only checks self-lock, both tasks end > up blocked on each other after T2. And task_is_blocked() is true for both > tasks, try_to_block_task() would keep them on runqueue with > tsk->is_blocked set. So if pick_next_task() picks A or B, > find_proxy_task() will stuck walking on A -> B -> A -> ... with rq->lock. > > Could we handle cycles in find_proxy_task(), or add a chain walk for > deadlock detection for FUTEX_LOCK_PING like rtmutex? https://lore.kernel.org/lkml/20260714152220.4046736-1-soolaugust@gmail.com/ -- Thanks and Regards, Prateek