On Thu, Oct 27, 2022 at 10:27:28AM +0800, Hao Sun wrote: > Hi, > > The following warning can be triggered with the C reproducer in the link. > Syzbot also reported this several days ago, Jiri posted a patch that > uses bpf prog `active` field to fix this by 05b24ff9b2cfab (bpf: > Prevent bpf program recursion...) according to syzbot dashboard > (https://syzkaller.appspot.com/bug?id=179313fb375161d50a98311a28b8e2fc5f7350f9). > But this warning can still be triggered on 247f34f7b803 > (Linux-v6.1-rc2) that already merged the patch, so it seems that this > still is an issue. > > HEAD commit: 247f34f7b803 Linux 6.1-rc2 > git tree: upstream > console output: https://pastebin.com/raw/kNw8JCu5 > kernel config: https://pastebin.com/raw/sE5QK5HL > C reproducer: https://pastebin.com/raw/X96ASi27 hi, right, that fix addressed that issue for single bpf program, and it won't prevent if there are multiple programs hook on contention_begin tracepoint and calling bpf_trace_printk, I'm not sure we can do something there.. will check do you run just the reproducer, or you load the server somehow? I cannot hit the issue so far thanks, jirka > > ------------[ cut here ]------------ > WARNING: CPU: 6 PID: 6850 at kernel/bpf/helpers.c:770 > try_get_fmt_tmp_buf kernel/bpf/helpers.c:770 [inline] > WARNING: CPU: 6 PID: 6850 at kernel/bpf/helpers.c:770 > bpf_bprintf_prepare+0xf6a/0x1170 kernel/bpf/helpers.c:818 > Modules linked in: > CPU: 6 PID: 6850 Comm: a.out Not tainted 6.1.0-rc2-dirty #23 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > 1.13.0-1ubuntu1.1 04/01/2014 > RIP: 0010:try_get_fmt_tmp_buf kernel/bpf/helpers.c:770 [inline] > RIP: 0010:bpf_bprintf_prepare+0xf6a/0x1170 kernel/bpf/helpers.c:818 > Code: c6 e8 ba 51 00 07 83 c0 01 48 98 48 01 c5 48 89 6c 24 08 e8 b8 > 0a eb ff 8d 6b 02 83 44 24 10 01 e9 2d f5 ff ff e8 a6 0a eb ff <0f> 0b > 65 ff 0d 85 bf 7c 7e bf 01 00 00 00 41 bc f0 ff ff ff e8 2d > RSP: 0018:ffffc90015a96c20 EFLAGS: 00010046 > RAX: 0000000000000000 RBX: 0000000000000002 RCX: ffff88814f8057c0 > RDX: 0000000000000000 RSI: ffff88814f8057c0 RDI: 0000000000000002 > RBP: ffffc90015a96d50 R08: ffffffff818681ba R09: 0000000000000003 > R10: 0000000000000005 R11: fffffbfff1a25ab2 R12: 0000000000000003 > R13: 0000000000000004 R14: ffffc90015a96e08 R15: 0000000000000003 > FS: 00007f012f4d2440(0000) GS:ffff8880b9d80000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f012f19ac28 CR3: 0000000148da3000 CR4: 0000000000350ee0 > Call Trace: > <TASK> > ____bpf_trace_printk kernel/trace/bpf_trace.c:385 [inline] > bpf_trace_printk+0xab/0x420 kernel/trace/bpf_trace.c:376 > bpf_prog_0605f9f479290f07+0x2f/0x33 > bpf_dispatcher_nop_func include/linux/bpf.h:963 [inline] > __bpf_prog_run include/linux/filter.h:600 [inline] > bpf_prog_run include/linux/filter.h:607 [inline] > __bpf_trace_run kernel/trace/bpf_trace.c:2254 [inline] > bpf_trace_run2+0x14d/0x3d0 kernel/trace/bpf_trace.c:2293 > __bpf_trace_contention_begin+0xb5/0xf0 include/trace/events/lock.h:95 > __traceiter_contention_begin+0x56/0x90 include/trace/events/lock.h:95 > trace_contention_begin include/trace/events/lock.h:95 [inline] > __pv_queued_spin_lock_slowpath+0x542/0xff0 kernel/locking/qspinlock.c:405 > pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:591 [inline] > queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline] > queued_spin_lock include/asm-generic/qspinlock.h:114 [inline] > do_raw_spin_lock+0x204/0x2d0 kernel/locking/spinlock_debug.c:115 > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline] > _raw_spin_lock_irqsave+0x41/0x50 kernel/locking/spinlock.c:162 > ____bpf_trace_printk kernel/trace/bpf_trace.c:390 [inline] > bpf_trace_printk+0xcf/0x420 kernel/trace/bpf_trace.c:376 > </TASK> > > Regards > Hao Sun
