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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?n/tI6GCrDtZEFaiuiUfb2Xw048a2KIB7y+S1pK8Fu7z7qT8ZbQ/Pzehs1Lbn?= =?us-ascii?Q?4hz9Gp1B3F0Giso2YpSRku2/0kRYqZ6u5HIybRb8Y0Mn8TsILOQedSqPl1CL?= =?us-ascii?Q?6w/CTIYNzx/bzUlzpRUFS3qpnssFCF7Bvq/JXz4okhaEuEIXyOsvGk1dc7xJ?= =?us-ascii?Q?gDIbdlLRQfPhWkxCQUWD6TwjXmCJYG01Cg4KjXibQt0bpB/IfdGsnEbsUCDJ?= =?us-ascii?Q?xdpeXb+8Kt0RoLROhj/ph4s3f9lczmgVwEuMXXADE4dr9MC21ZtJ20SeDIWP?= =?us-ascii?Q?gYQ6WljTez9qQbx1X7s0MjJEJG2cSwkXbMkj0n5NNmvG6PpXc5SYaaZi/KFv?= =?us-ascii?Q?JFfd02Z5mMv1E0iMihU+/PVpu76vFNTl03xn5NIrKjbUEA2bdLwoV18c5zSN?= =?us-ascii?Q?mQDKLF6Rf+31+ahDgztPiBj7xpQiUocXAiIO/fQNCDeMkQutrShU5pdpYbh/?= =?us-ascii?Q?5aPLT40Z3ZpjvFgQ/vxj8X7lBVY4jH7RMniMObxzLJhZXueeCe/KTvidhu98?= =?us-ascii?Q?EgxRrcwsBzBouw4FryFjm7e6GV8zYNxlDXuBDmbNcs8rzoe/EuIaXoUclHSK?= =?us-ascii?Q?eYV802SmxAS84mTO+Y6Z1/dUSof9Fx3kN3TgZrknc2hetUCy70grTpJOGxUO?= =?us-ascii?Q?GXtaFRwuFt9twKVdsdBNCD/ZyFn8ZL8Lw5SlD5+PIdFx4+uW3bQCYgiYYVXR?= =?us-ascii?Q?0zGfu0zBNQ9MNUB0tog5CicmrMMispe05uLhpnvw7tieXUPip8N6y3I7uEmm?= =?us-ascii?Q?ivZmNgq3QMKHrctPdt5Ovt0/G7e4Hks0DIi6g1PAtEwznd8bE4LvDUTZzX9T?= =?us-ascii?Q?ancRHtjqVTSevHoh2B0XU2yrkGRw56fm+46lF797+v8OlaY1EBjBlkwSnjmp?= =?us-ascii?Q?ectHKGPeti6RDre5atF0jGanJxQVkYmUHQmMXq0rcSKI/Cg6ktGnXV8lf/SY?= =?us-ascii?Q?m/KRblqMpby/HaQQM/fmzQVdlh21pVBcpW3LpWBU24a4wj6+ZuzNTsrpBZ9S?= =?us-ascii?Q?8ZZxV/HdnG7kILE4wKaTVhBReX/bCfXDyXghWkLWDBp/Th6KM6ElGU4fp3Yo?= =?us-ascii?Q?VnHc6GLKSzUvf5PMU9eErFljD9YHwPZ9AgXOquU3a8VmDny3yNBoC3gy2piO?= =?us-ascii?Q?klm7Si5TRBM6E9LJ113gfS3lxqdIjy8lQLd+L82B9Y/g8jT6hRQv+NZppyBC?= =?us-ascii?Q?rBV4tkbhoxGC3jHrgHTMm8NoP7i47rtpELPemuF8uwZ8NJiWqdZ5O1wncuBz?= =?us-ascii?Q?FziQYE43Xhn+AcdJTuTbnV1uWSA36SLU9OAtprNYCznzAPlvaCE/5jFp9iDl?= =?us-ascii?Q?+55uorEUEnkPxrcBJ8QN6FAAJIIyWW6fG5ZQoFQoYuromGr4fpjvl1GsFvi/?= =?us-ascii?Q?1GSzuF9i4WZjeSlRbqvm1rwm/Wa/vzcXe/PSUimXRuwiRmukbaxt1wtZmFVe?= =?us-ascii?Q?cSMWFmTi3yx8zEJxJL4wz2/0kFf7GGZIFLbvmrKp3RV+w3jmuqbKElZkGfXJ?= =?us-ascii?Q?r0fF/GWDYeo2ipCLUlwwzQn67e65pI8A2D12gjeexogZDbUcIxLiIx61qatu?= =?us-ascii?Q?x+ksCFOGxiD5odfDRZyMLTKGQ4udoYSBvjMZ2+2l?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: f11ba13d-b984-49a7-2cb6-08dd6d154625 X-MS-Exchange-CrossTenant-AuthSource: CY5PR12MB6405.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Mar 2025 09:53:49.9115 (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: Wk8t1zj3++3QQ3xX/VlAOHdAxn9wqaNXurX5fIGXtwr2hViu2H8YBSyRU2mbCMw920SHNmsbSemJkljlSjJlyg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR12MB7183 On Thu, Mar 27, 2025 at 08:56:12AM +0100, Andrea Righi wrote: > On Wed, Mar 26, 2025 at 02:24:16PM -1000, Tejun Heo wrote: > > Hello, Andrea. > > > > On Tue, Mar 25, 2025 at 03:00:21PM +0100, Andrea Righi wrote: > > > @@ -7114,12 +7114,22 @@ __bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf) > > > > > > if (ops_cpu_valid(cpu, NULL)) { > > > struct rq *rq = cpu_rq(cpu); > > > + struct rq_flags rf; > > > + bool rq_unlocked; > > > + > > > + preempt_disable(); > > > + rq_unlocked = (rq != this_rq()) || scx_kf_allowed_if_unlocked(); > > > + if (rq_unlocked) { > > > + rq_lock_irqsave(rq, &rf); > > > > I don't think this is correct: > > > > - This is double-locking regardless of the locking order and thus can lead > > to ABBA deadlocks. > > > > - There's no guarantee that the locked rq is this_rq(). e.g. In wakeup path, > > the locked rq is on the CPU that the wakeup is targeting, not this_rq(). > > > > Hmm... this is a bit tricky. SCX_CALL_OP*() always knows whether the rq is > > locked or not. We might as well pass it the currently locked rq and remember > > that in a percpu variable, so that scx_bpf_*() can always tell whether and > > which cpu is rq-locked currently. If unlocked, we can grab the rq lock. If > > the traget cpu is not the locked one, we can either fail the operation (and > > trigger ops error) or bounce it to an irq work. > > Hm... that's right, it looks like this requires a bit more work than > expected, but saving the currently locked rq might be helpful also for > other kfuncs, I'll take a look at this. What if we lock the rq in the scx_kf_allowed_if_unlocked() case, and for all the other cases we ignore locking if rq == this_rq(). If we need to operate on a different rq than the current one we could either defer the work or just trigger an ops error. Something like: if (scx_kf_allowed_if_unlocked()) { rq_lock_irqsave(rq, &rf); update_rq_clock(rq); } else if (rq != this_rq()) { // defer work or ops error return; } lockdep_assert_rq_held(rq); rq->scx.cpuperf_target = perf; cpufreq_update_util(rq, 0); if (scx_kf_allowed_if_unlocked()) rq_unlock_irqrestore(rq, &rf); AFAICS all the current scx schedulers call scx_bpf_cpuperf_set() from ops.running(), ops.tick() or ops.init(), so even with the ops error we should cover all the existent cases. The only unsupported scenario is calling scx_bpf_cpuperf_set() from ops.enqueue() / ops.select_cpu(), but maybe we could add the deferred work later to handle that if needed. Thanks, -Andrea