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The donor > > does not execute there, and its original execution CPU remains recorded > > in wake_cpu. > > > > set_task_cpu() warns unconditionally for migration-disabled tasks, so a > > subsequent proxy migration or the wakeup path returning the donor home > > triggers a false positive. Moving a blocked scheduling context does not > > violate the migration-disabled execution context. > > > > Exclude blocked proxy donors from the warning. The proxy wakeup path > > restores an executable placement before clearing the blocked state. > > > > This is a preparatory fix for enabling proxy execution together with > > sched_ext. > > > > Signed-off-by: Andrea Righi > > Nice catch on this! > > I'm wondering why I've not tripped this myself yet. Is > migration_disabled set more often in the sched_ext paths? Or was there > a specific workload that you hit this with? I triggered this with a modified scx_cosmos with proxy-exec support (option --proxy-exec): https://github.com/sched-ext/scx/tree/cosmos-proxy-exec This was the trace, triggered when scx_cosmos was stopped: [ 12.992201] WARNING: kernel/sched/core.c:3444 at set_task_cpu+0x1d3/0x280, CPU#6: kworker/u65:1/103 [ 12.992387] Modules linked in: [ 12.992593] CPU: 6 UID: 0 PID: 103 Comm: kworker/u65:1 Not tainted 7.1.0-virtme #3 PREEMPT(full) [ 12.993012] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 12.993075] Workqueue: events_unbound bpf_map_free_deferred [ 12.993139] RIP: 0010:set_task_cpu+0x1d3/0x280 [ 12.993285] Code: 14 89 6b 64 c6 83 09 17 00 00 01 5b 41 5e 41 5f 5d c3 cc cc cc cc cc 90 0f 0b 90 66 83 bb 80 05 00 00 00 0f 84 f8 fe ff ff 90 <0f> 0b 90 e9 ef fe ff ff 48 8d 3d ce 12 4c 02 67 48 0f b9 3a e9 03 [ 12.993656] RSP: 0018:ffffc900003f7cf8 EFLAGS: 00010002 [ 12.994642] RAX: 0000000000000000 RBX: ffff888100c6c800 RCX: 0000000000000046 [ 12.994756] RDX: ffffc900003f7d2c RSI: ffff888100c6d338 RDI: ffff888100c454d0 [ 12.994860] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 [ 12.994956] R10: 000000000000003b R11: ffffffff813f5c30 R12: 0000000000000000 [ 12.995055] R13: ffff888100c6d320 R14: ffff888100c44800 R15: 0000000000000206 [ 12.995167] FS: 0000000000000000(0000) GS:ffff8882b380a000(0000) knlGS:0000000000000000 [ 12.995273] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 12.995354] CR2: 00007fe19b902000 CR3: 000000000364c000 CR4: 0000000000750ef0 [ 12.995462] PKRU: 55555554 [ 12.995502] Call Trace: [ 12.995540] [ 12.995580] try_to_wake_up+0x360/0x6f0 [ 12.995640] __mutex_unlock_slowpath+0x32f/0x540 [ 12.995716] ? bpf_local_storage_map_free+0x84/0x280 [ 12.995789] ? process_scheduled_works+0x225/0x520 [ 12.995861] bpf_local_storage_map_free+0x257/0x280 [ 12.995934] bpf_map_free+0x84/0x110 [ 12.995992] process_scheduled_works+0x271/0x520 [ 12.996071] worker_thread+0x1e1/0x300 [ 12.996133] ? __pfx_worker_thread+0x10/0x10 [ 12.996206] kthread+0x10c/0x140 [ 12.996266] ? __pfx_kthread+0x10/0x10 [ 12.996319] ret_from_fork+0x189/0x330 [ 12.996378] ? __pfx_kthread+0x10/0x10 [ 12.996435] ret_from_fork_asm+0x1a/0x30 [ 12.996500] Looking at bpf_local_storage_map_free(), I think I triggered this warning, because bpf_map_free() calls migrate_disable() around map->ops->map_free() and the deferred map-free workers can block on mutexes while migration is disabled. Then proxy-exec moves the worker to the mutex owner's CPU and when the mutex is released, ttwu returns the worker to its pinned CPU and trips the set_task_cpu() warning. > > Acked-by: John Stultz > > thanks > -john Thanks, -Andrea