On Thu, Apr 29, 2021 at 11:28:34PM +0200, Jiri Olsa wrote: > For functions with variable arguments like: > > void set_worker_desc(const char *fmt, ...) > > the BTF data contains void argument at the end: > > [4061] FUNC_PROTO '(anon)' ret_type_id=0 vlen=2 > 'fmt' type_id=3 > '(anon)' type_id=0 > > When attaching function with this void argument the btf_distill_func_proto > will set last btf_func_model's argument with size 0 and that > will cause extra loop in save_regs/restore_regs functions and > generate trampoline code like: > > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 48 83 ec 10 sub $0x10,%rsp > 53 push %rbx > 48 89 7d f0 mov %rdi,-0x10(%rbp) > 75 f8 jne 0xffffffffa00cf007 > ^^^ extra jump > > It's causing soft lockups/crashes probably depends on what context > is the attached function called, like for set_worker_desc: > > watchdog: BUG: soft lockup - CPU#16 stuck for 22s! [kworker/u40:4:239] > CPU: 16 PID: 239 Comm: kworker/u40:4 Not tainted 5.12.0-rc4qemu+ #178 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-1.fc33 04/01/2014 > Workqueue: writeback wb_workfn > RIP: 0010:bpf_trampoline_6442464853_0+0xa/0x1000 > Code: Unable to access opcode bytes at RIP 0xffffffffa3597fe0. > RSP: 0018:ffffc90000687da8 EFLAGS: 00000217 > Call Trace: > set_worker_desc+0x5/0xb0 > wb_workfn+0x48/0x4d0 > ? psi_group_change+0x41/0x210 > ? __bpf_prog_exit+0x15/0x20 > ? bpf_trampoline_6442458903_0+0x3b/0x1000 > ? update_pasid+0x5/0x90 > ? __switch_to+0x187/0x450 > process_one_work+0x1e7/0x380 > worker_thread+0x50/0x3b0 > ? rescuer_thread+0x380/0x380 > kthread+0x11b/0x140 > ? __kthread_bind_mask+0x60/0x60 > ret_from_fork+0x22/0x30 > > This patch is removing the void argument from struct btf_func_model > in btf_distill_func_proto, but perhaps we should also check for this > in JIT's save_regs/restore_regs functions. actualy looks like we need to disable functions with variable arguments completely, because we don't know how many arguments to save I tried to disable them in pahole and it's easy fix, will post new fix jirka