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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?V/fIKylddw13lhNC0BlbmwZMJf5uv+6+YHwS1eb54g89bxWyrAmRWRsPBIEG?= =?us-ascii?Q?Fz/0evcw6pQ4I//F03eikuOLeWJC+0ql7wKGjes5OxPTfXukEPD0VlcTqsXg?= =?us-ascii?Q?YnIUX5uLtvqqlHHcawIvXyESW+X0isLX9zinfeF41QAw6Mp5TEYx6aIOMsSB?= =?us-ascii?Q?pS40kRxHrH+4xpVqLQSvQP3epTDM5L8rwSjsKQtAelBBeozN2gNrIPx4bXTU?= =?us-ascii?Q?uOKFKbqGuMa7JihWMjCWTcAEVW8A2IX8y+s2i8aKNdUJh2p7H6AH0ZEnOefT?= =?us-ascii?Q?3dph8FxM4H++os+LCNLGuVqONh/SW9VicJT6jhDycC6ucb9u5IcSQ1ijhh99?= =?us-ascii?Q?hjLCsqcjY+2BdZY/o6Rts2Kj4QASitcPSXZsZcj4e8cmO+R0pT2wvSc6X+zb?= =?us-ascii?Q?BuVTP4cec2bqZlcVWOQ1WvlFUmoNxewsHdCCJyQo0qvp30dJboIYGl2YLA7y?= =?us-ascii?Q?yJ3U9BPfi73JGuEjqCKr6xIN0OgfvF4CfqvxMama5WB9oRk9/GLW8FHr+2Hx?= =?us-ascii?Q?/0yh3yUstAgy/O73QAmLGQRvwvbpqNr8JNI4r/z2VYF92A5Cqv9ozwfIrkaP?= =?us-ascii?Q?oNfuNdYgY3clFUU2o3vdzwJbbxx5MqT+UriSiOy7uo3uJGnq2RnLahfA6Y2V?= =?us-ascii?Q?q8bLWoiiQYvVh2az7ZaA6vR7yf+A8IR0TJfVODp5mbLFErjoyf72r1IT72Q8?= =?us-ascii?Q?KWqIwquGCGxqz7p0yRQMYMNNritD0mx9dJitCfGTx2BsQdH4w4WZ5wT6zC2E?= =?us-ascii?Q?QCNkuC2UHSlZn+bll8PCvBPC0UfQJaeMn0w2fmptjjfewc6/F+WomCyzjxMD?= =?us-ascii?Q?5VHZOR068/T9UhlTwj/q/uDkgf+pi0tnMxpxIIfV396LhrI2dDxvOy4oJ9sL?= =?us-ascii?Q?B3HV6r1JETU0F6dW2DOklQuLyOftOWSa6/nldKA45QKrrv+xZfJiyef/70L4?= =?us-ascii?Q?RFuBUHjpgGzxxaqo3veV6KlQ8h7K+EQ/d+jLWtgj38Rg7Z3Wgt3K9ITkFu6n?= =?us-ascii?Q?f0bKTKyojcn6AkUQmqgw6jX2nFj20uo09Sk+tJv4FvTvGpMgMPSZFT3DtzB6?= =?us-ascii?Q?SUtykRwfvhd9zXWiBDdz4jFSadnkXWKP+WwGw1+cVMdtsTRCfPy5Ar4GFibw?= =?us-ascii?Q?rS6bS/5e4kiF7FjN08mRrw7iYC86OoAKl1uTVcHSMgkktHE0e1qC9yKsLgk6?= =?us-ascii?Q?BANmX7TS9iTl6k47gy7F8MV3E34cJ7ubJ9f/7MGpcCC+VfWIX4pBfpGExwG8?= =?us-ascii?Q?N3wo0Q+yZt48dhcDYuw6hS4rukjmIGXHOuWip+0KrAsfX0awlgbU8DtQesU/?= =?us-ascii?Q?YjbnNVCSx5bmruLvqr2s8P8mTDJZyqPsAXGV3F9tnXW4mtOxqgwpkkUdeXXZ?= =?us-ascii?Q?xhugZBy6PKj+rMd1WFXo2G0uSXsQrCpuQkKXrKQzB+6lQwARPxptUqtBxXYe?= =?us-ascii?Q?WSEr57HTJ9DwUkuGomf8uDSB4xQu+aOyxh9puZk1ponHqTLJaV7VYUAu5E0s?= =?us-ascii?Q?alMXW8fHYc+H76kHB121s7oYzCtfu7F1/rv/uR3bCWAru0UlLDY1oXjuRaDU?= =?us-ascii?Q?mi2xltQpQbgUVnu8rLG4AVYjEvOppCFx8gQkAue+80Cu9GN9Ovq85bYny2Yl?= =?us-ascii?Q?5fYGeq1cBB4iExovpSCBhfE2aRoxpy0Ka6PB2oTm3pfgAWkXqezUq30LNulb?= =?us-ascii?Q?QYhLz5yK/yEC56Z7aqq7m2lRjgRAtSDb8gy0vV9NC8lqSfAi?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 704df23c-238e-472f-9c44-08df2c8c263c X-MS-Exchange-CrossTenant-AuthSource: BL1PR12MB5174.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Oct 2026 20:20:56.0165 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 7OLb0wyhRGnmMh1SttnjM5gdhC/c5OwOZCNhfuTC6V9ckAXGlvEnbyf1DYfT9phCI1sd7Gyx5+zJ25KfEZMfuA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB7522 The SCX_KICK_WAIT wait is deferred to rq->scx.kick_sync_bal_cb, which a final pick queues on the local rq. Under core scheduling, a pick that returns a task isn't final: pick_next_task() goes on to pick the SMT siblings, and their dispatch can release the shared rq lock with the callback still queued. A CPU acquiring the rq lock in that window then finds a pending balance callback and triggers the warning in rq_pin_lock(). Unlike the deferred work, the kick_sync wait can't be moved to irq_work, since it needs to wait with IRQs enabled. However, during a core-wide selection the rq lock is only released by a dispatch, which already restarts the selection through lock_drop_seq. Fix this by taking the kick_sync callback off the local rq before each dispatch of the selection. If the rq lock isn't released, queue it again right away. Otherwise, set kick_sync_pending again, so that the next final pick of this CPU queues it, as done for a non-core pick that returns RETRY_TASK. Fixes: 415cb193bb97 ("sched_ext: Fix SCX_KICK_WAIT deadlock by deferring wait to balance callback") Cc: stable@vger.kernel.org # v7.0+ Suggested-by: Tejun Heo Signed-off-by: Andrea Righi --- kernel/sched/ext/ext.c | 43 +++++++++++++++++++++++++++++++++++++++++- 1 file changed, 42 insertions(+), 1 deletion(-) diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c index 0c5ed97c4d080..2348d5b72eb26 100644 --- a/kernel/sched/ext/ext.c +++ b/kernel/sched/ext/ext.c @@ -3369,6 +3369,28 @@ static enum scx_dsp_verdict dispatch_pick(struct rq *rq, struct rq_flags *rf, } #ifdef CONFIG_SCHED_CORE +/* + * Take @head off @rq's balance callbacks if it's queued. Returns whether it + * was queued. + */ +static bool dequeue_balance_callback(struct rq *rq, struct balance_callback *head) +{ + struct balance_callback **pprev; + + lockdep_assert_rq_held(rq); + + for (pprev = &rq->balance_callback; *pprev; pprev = &(*pprev)->next) { + if (*pprev != head) + continue; + + *pprev = head->next; + head->next = NULL; + return true; + } + + return false; +} + /* * Dispatch for a pick when core scheduling is enabled. The selection picks for * all SMT siblings and the rq_i->core_pick state it builds must stay atomic @@ -3379,8 +3401,10 @@ static enum scx_dsp_verdict dispatch_pick(struct rq *rq, struct rq_flags *rf, static enum scx_dsp_verdict dispatch_core_pick(struct rq *rq, struct rq_flags *rf, struct task_struct *prev) { + struct rq *this_rq = this_rq(); enum scx_dsp_verdict verdict; u32 seq = rq->scx.lock_drop_seq; + bool kick_sync_queued; /* another dispatch is in flight on @rq, let that handle it */ if (rq->scx.flags & SCX_RQ_IN_DISPATCH) @@ -3388,6 +3412,16 @@ static enum scx_dsp_verdict dispatch_core_pick(struct rq *rq, struct rq_flags *r rq_unpin_lock(rq, rf); + /* + * dispatch_one() can release the rq lock while the selection is in + * progress (see below), so this CPU's kick_sync wait queued by an + * earlier pick of the selection can't stay queued across it. Take it + * off and queue it again if the rq lock isn't released. Otherwise, the + * selection restarts, so leave it pending for the next final pick of + * this CPU. + */ + kick_sync_queued = dequeue_balance_callback(this_rq, &this_rq->scx.kick_sync_bal_cb); + verdict = dispatch_one(rq, prev); /* @@ -3409,8 +3443,15 @@ static enum scx_dsp_verdict dispatch_core_pick(struct rq *rq, struct rq_flags *r rq_repin_lock(rq, rf); /* if dispatch_one() released the rq lock, restart the selection */ - if (rq->scx.lock_drop_seq != seq) + if (rq->scx.lock_drop_seq != seq) { + if (kick_sync_queued) + this_rq->scx.kick_sync_pending = true; return SCX_DSP_RETRY; + } + + if (kick_sync_queued) + queue_balance_callback(this_rq, &this_rq->scx.kick_sync_bal_cb, + kick_sync_wait_bal_cb); return verdict; } -- 2.56.0