systemd-services: setting conflict between schedulers

[sirlucjan]

Together with @arighi , we have figured out that there is a specific bug in Ubuntu - when installing the apt/systemd tries to activate all schedulers simultaneously. The consequences of this error are as follows:

[22053.942960] BUG: kernel NULL pointer dereference, address: 0000000000000000
[22053.942966] #PF: supervisor write access in kernel mode
[22053.942968] #PF: error_code(0x0002) - not-present page
[22053.942969] PGD 0 P4D 0 
[22053.942972] Oops: 0002 [#1] PREEMPT SMP NOPTI
[22053.942976] CPU: 6 PID: 3550 Comm: sched_ext_ops_h Tainted: G           O       6.7.0-4-generic #4+scx3-Ubuntu
[22053.942978] Hardware name: GPD G1621-02/G1621-02, BIOS 2.04 09/01/2022
[22053.942980] Sched_ext: central (enabled+all)
[22053.942981] RIP: 0010:scx_ops_disable_workfn+0x85/0x610
[22053.942987] Code: 89 df f3 48 ab b9 01 00 00 00 83 fa 01 0f 86 c3 00 00 00 89 d0 f0 0f b1 0d 60 ff 11 02 0f 85 10 05 00 00 48 8b 85 90 fe ff ff <89> 10 81 fa 00 04 00 00 0f 84 ef 04 00 00 0f 8e cb 00 00 00 48 c7
[22053.942989] RSP: 0018:ffffad420257fd30 EFLAGS: 00010246
[22053.942991] RAX: 0000000000000000 RBX: ffffad420257fd58 RCX: 0000000000000001
[22053.942993] RDX: 0000000000000040 RSI: 0000000000000000 RDI: ffffad420257fd98
[22053.942994] RBP: ffffad420257fea8 R08: 0000000000000000 R09: 0000000000000000
[22053.942996] R10: 0000000000000000 R11: 0000000000000000 R12: ffffad420257fd98
[22053.942998] R13: ffff96a4d07eddc0 R14: ffff96a4d07eddc4 R15: ffffffff8897c3b0
[22053.942999] FS:  0000000000000000(0000) GS:ffff96a7dfb00000(0000) knlGS:0000000000000000
[22053.943002] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[22053.943003] CR2: 0000000000000000 CR3: 00000001f6a3c001 CR4: 0000000000f70ef0
[22053.943005] PKRU: 55555554
[22053.943006] Call Trace:
[22053.943008]  <TASK>
[22053.943012]  ? show_regs+0x6d/0x80
[22053.943016]  ? __die+0x24/0x80
[22053.943018]  ? page_fault_oops+0x99/0x1b0
[22053.943021]  ? do_user_addr_fault+0x2ee/0x6b0
[22053.943024]  ? exc_page_fault+0x83/0x1b0
[22053.943028]  ? asm_exc_page_fault+0x27/0x30
[22053.943030]  ? __pfx_scx_ops_disable_workfn+0x10/0x10
[22053.943034]  ? scx_ops_disable_workfn+0x85/0x610
[22053.943036]  ? asm_sysvec_irq_work+0x1b/0x20
[22053.943042]  ? __pfx_scx_ops_disable_workfn+0x10/0x10
[22053.943043]  kthread_worker_fn+0x9e/0x230
[22053.943048]  ? __pfx_kthread_worker_fn+0x10/0x10
[22053.943050]  kthread+0xef/0x120
[22053.943053]  ? __pfx_kthread+0x10/0x10
[22053.943056]  ret_from_fork+0x44/0x70
[22053.943058]  ? __pfx_kthread+0x10/0x10
[22053.943061]  ret_from_fork_asm+0x1b/0x30
[22053.943064]  </TASK>

To prevent the user from running several services at the same time, it is worth thinking about such a temporary solution. Ultimately, I would like to create one systemd service that would run a specific scheduler.

[Byte-Lab]

Merging, but this crash also shouldn't have happened. Is this a known issue?

[sirlucjan]

@arighi can make an opinion on this issue, I have not experienced it. I just wanted to prevent this error from occurring until it is fixed.

[htejun]

Can you map scx_ops_disable_workfn+0x85 to line using scripts/faddr2line vmlinux 'scx_ops_disable_workfn+0x85'

[arighi]

Sorry, I'm reading this only now, I just sent PR (sched-ext/sched_ext#129) that has more details about the bug.