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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?tZtzQWCY7TgqHs2541ABbxkkZD/rAuXtsfZzCtNmc+cW13fNKL9B+/nrAKD0?= =?us-ascii?Q?Ei6irVcJ8Knxtk/6uI2UxxEV2oVqp8y5FNEFYMSKB4TRkZjmiCOhL5EuWyY2?= =?us-ascii?Q?e3PR/l4gd0vwGSHIHVygi3OTI5fX58NJzgTKwk+Tftgf6Fa981S7wLv89wGH?= =?us-ascii?Q?poi56zEitRylZOBbZyepls9yNtcTgFB8clyoLQ/vzBhKrnve6PblAOE3rnUm?= =?us-ascii?Q?suY++CDlPyLLxLf1wjIjCDrOSdbLUeXnoceQlJEjspTxlnl3N+TFp8MA1vvx?= =?us-ascii?Q?OrwORpP9sZcb16L443bIynTr/T1pRFvlgzUnkkPvHvUCxKYQfLNKz8enfZFl?= =?us-ascii?Q?BwQZTEU6Rbjhv0go4tNilcX43ARoDGDoW8bSKG7CqnW+/JKNjh6zwREr1yVX?= =?us-ascii?Q?OSfA+DY2e44kiQxejY0bco3IzigjHsEyPIaCOghe/bFz+0KCk+AYaemnJn4Y?= =?us-ascii?Q?joPFsVapPB18VxEhU7+YMZA9yRpFllgdwFJXbSBOQ7gOdqLcHH+sQBHuMqIB?= =?us-ascii?Q?HBkigxemHLxtzenNwvGmN0U7WPiZ3US0gxwOV3AyrNFn1P1YONoqE+QCIlCg?= =?us-ascii?Q?+qHYfItUW1eYMoX4YMUikJHGto860/UAhpYR0r8IOndMH9DmvQGIkUDDMk1L?= =?us-ascii?Q?lbr6b/M+BopFdKAIklauIXDjX1REAyMTKgs3/UmD2zNW+JS0Jp2OO0mTOxeN?= =?us-ascii?Q?nvNJJAz1DG/9Q2Yqj+pGEg3c92FEutKV4zH2KXbmsBmkuS60pOONlP0Qozz9?= =?us-ascii?Q?NS5Ga6b1JxPq6c4el4W2Jy3voSz4Bie/wK7r0o+S3SgGiWAjI7MMWG8IViuF?= =?us-ascii?Q?4CEKaFsAFfyZbwd8J0/rT+ab9EiUkOwOzu4CIWORX+dfpF/60ksGTv+IHFqc?= =?us-ascii?Q?1EdndV1cwztGjky3k+wjaCKYZ8+TPOSb0x4Vn1ojPf++I/YKJkzWrl21V5mR?= =?us-ascii?Q?7kAc0Xp/lPRQ+r/rOcZR4L8cLR0jbfDaOHJfxGskUC4/1mQEAORjEGvqxPOt?= =?us-ascii?Q?JmfiZQGqrJAIWNT1/fg9p26b4mqcnNUajx+j9+PhSZBygQBlLytjFPHSqVGu?= =?us-ascii?Q?bHmbb1MKlYicVoCZQ13MKz29x+nUG2JoqzoXaFCSiHUPfksbzAEUAB+3E62n?= =?us-ascii?Q?Y87XtO8MHhRwWPG3ldQoVChjAYIHPKHSICw5IoR/OEccbznbY8tGiPDVve77?= =?us-ascii?Q?l96ulbHIuXFYF7y97lgu7rtp9Nbwq5lHXmV5rLevYenH+m91g149nlobyerK?= =?us-ascii?Q?VOxIPR/4sSVkAelW4f9RV0xVFGDS81RlOme07HgFy385Qw9+Ntsd8mU7AEzL?= =?us-ascii?Q?tfF/VT0OWPtIq3jsCHb7GJUA3vMz8QnDXq6wYsVLKTqdFgkG/7QlERUhdG9D?= =?us-ascii?Q?ti7nVdhxbL5QSgGJBuvkST2Yjc5PWRntumNMv3OswPbvu9edrghRZ7jJGR+X?= =?us-ascii?Q?QX6SFt+G4NLQmQrBDc2mLe18yVc3Hab5iZnh9UU3AoyD7SDYseO2K10C/0M6?= =?us-ascii?Q?g+dXqZZK617srRDDhzrX2ElaL45P1ZwvsEK4w0Momy9PMY4vxjfUQrY9RZOZ?= =?us-ascii?Q?U6u5M8I1b1Bp7F3P8qzTTChIfHIxtL3larIKtYqE?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: e141d4d7-fcd1-4cac-bbcd-08dd6d04d6fc X-MS-Exchange-CrossTenant-AuthSource: CY5PR12MB6405.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Mar 2025 07:56:11.2603 (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: xlGxQMYf4as3t98/splLfU1VmrDDC/EfRa8mJQEmlq5Xv8mmcPeMj/1/SNKXJ6XZp+0YV7vcOm0BQjHGzMN4wA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY5PR12MB6455 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. Thanks! -Andrea