Re: [PATCH] perf: Fix missing SIGTRAPs

From: Marco Elver
Date: Thu Oct 06 2022 - 10:00:25 EST

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On Thu, Oct 06, 2022 at 03:33PM +0200, Peter Zijlstra wrote:
>
> OK, so the below seems to pass the concurrent sigtrap_threads test for
> me and doesn't have that horrible irq_work_sync hackery.
>
> Does it work for you too?

I'm getting this (courtesy of syzkaller):

| BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor.8/22848
| caller is perf_swevent_get_recursion_context+0x13/0x80
| CPU: 0 PID: 22860 Comm: syz-executor.6 Not tainted 6.0.0-rc3-00017-g1472d7e42f41 #64
| Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
| Call Trace:
| <TASK>
| dump_stack_lvl+0x6a/0x86
| check_preemption_disabled+0xdf/0xf0
| perf_swevent_get_recursion_context+0x13/0x80
| perf_pending_task+0xf/0x80
| task_work_run+0x73/0xc0
| do_exit+0x459/0xf20
| do_group_exit+0x3f/0xe0
| get_signal+0xe04/0xe60
| arch_do_signal_or_restart+0x3f/0x780
| exit_to_user_mode_prepare+0x135/0x1a0
| irqentry_exit_to_user_mode+0x6/0x30
| asm_sysvec_irq_work+0x16/0x20

That one I could fix up with:

| diff --git a/kernel/events/core.c b/kernel/events/core.c
| index 9319af6013f1..2f1d51b50be7 100644
| --- a/kernel/events/core.c
| +++ b/kernel/events/core.c
| @@ -6563,6 +6563,7 @@ static void perf_pending_task(struct callback_head *head)
| * If we 'fail' here, that's OK, it means recursion is already disabled
| * and we won't recurse 'further'.
| */
| + preempt_disable_notrace();
| rctx = perf_swevent_get_recursion_context();
|
| if (event->pending_work) {
| @@ -6573,6 +6574,7 @@ static void perf_pending_task(struct callback_head *head)
|
| if (rctx >= 0)
| perf_swevent_put_recursion_context(rctx);
| + preempt_enable_notrace();
| }
|
| #ifdef CONFIG_GUEST_PERF_EVENTS

But following that, I get:

| ======================================================
| WARNING: possible circular locking dependency detected
| 6.0.0-rc3-00017-g1472d7e42f41-dirty #65 Not tainted
| ------------------------------------------------------
| syz-executor.11/13018 is trying to acquire lock:
| ffffffffbb754a18 ((console_sem).lock){-.-.}-{2:2}, at: down_trylock+0xa/0x30 kernel/locking/semaphore.c:139
|
| but task is already holding lock:
| ffff8ea992e00e20 (&ctx->lock){-.-.}-{2:2}, at: perf_event_context_sched_out kernel/events/core.c:3499 [inline]
| ffff8ea992e00e20 (&ctx->lock){-.-.}-{2:2}, at: __perf_event_task_sched_out+0x29e/0xb50 kernel/events/core.c:3608
|
| which lock already depends on the new lock.
|
| << snip ... lockdep unhappy we're trying to WARN >>
|
| WARNING: CPU: 3 PID: 13018 at kernel/events/core.c:2288 event_sched_out+0x3f2/0x410 kernel/events/core.c:2288
| Modules linked in:
| CPU: 3 PID: 13018 Comm: syz-executor.11 Not tainted 6.0.0-rc3-00017-g1472d7e42f41-dirty #65
| Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
| RIP: 0010:event_sched_out+0x3f2/0x410 kernel/events/core.c:2288
| Code: ff ff e8 21 b2 f9 ff 65 8b 05 76 67 7f 46 85 c0 0f 84 0f ff ff ff e8 0d b2 f9 ff 90 0f 0b 90 e9 01 ff ff ff e8 ff b1 f9 ff 90 <0f> 0b 90 e9 3b fe ff ff e8 f1 b1 f9 ff 90 0f 0b 90 e9 01 ff ff ff
| RSP: 0018:ffffa69c8931f9a8 EFLAGS: 00010012
| RAX: 0000000040000000 RBX: ffff8ea99526f1c8 RCX: ffffffffb9824d01
| RDX: ffff8ea9934a0040 RSI: 0000000000000000 RDI: ffff8ea99526f1c8
| RBP: ffff8ea992e00e00 R08: 0000000000000000 R09: 0000000000000000
| R10: 00000000820822cd R11: 00000000d820822c R12: ffff8eacafcf2e50
| R13: ffff8eacafcf2e58 R14: ffffffffbb62e9a0 R15: ffff8ea992e00ef8
| FS: 00007fdcddbb6640(0000) GS:ffff8eacafcc0000(0000) knlGS:0000000000000000
| CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
| CR2: 00007fdcddbb5fa8 CR3: 0000000112846004 CR4: 0000000000770ee0
| DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
| DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
| PKRU: 55555554
| Call Trace:
| <TASK>
| group_sched_out.part.0+0x5c/0xe0 kernel/events/core.c:2320
| group_sched_out kernel/events/core.c:2315 [inline]
| ctx_sched_out+0x35d/0x3c0 kernel/events/core.c:3288
| task_ctx_sched_out+0x3d/0x60 kernel/events/core.c:2657
| perf_event_context_sched_out kernel/events/core.c:3505 [inline]
| __perf_event_task_sched_out+0x31b/0xb50 kernel/events/core.c:3608
| perf_event_task_sched_out include/linux/perf_event.h:1266 [inline]
| prepare_task_switch kernel/sched/core.c:4992 [inline]
| context_switch kernel/sched/core.c:5134 [inline]
| __schedule+0x4f8/0xb20 kernel/sched/core.c:6494
| preempt_schedule_irq+0x39/0x70 kernel/sched/core.c:6806
| irqentry_exit+0x32/0x90 kernel/entry/common.c:428
| asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:649
| RIP: 0010:try_to_freeze include/linux/freezer.h:66 [inline]
| RIP: 0010:freezer_count include/linux/freezer.h:128 [inline]
| RIP: 0010:coredump_wait fs/coredump.c:407 [inline]
| RIP: 0010:do_coredump+0x1193/0x1b60 fs/coredump.c:563
| Code: d3 25 df ff 83 e3 08 0f 84 f0 03 00 00 e8 c5 25 df ff 48 f7 85 88 fe ff ff 00 01 00 00 0f 85 7e fc ff ff 31 db e9 83 fc ff ff <e8> a8 25 df ff e8 63 43 d3 ff e9 d2 f1 ff ff e8 99 25 df ff 48 85
| RSP: 0018:ffffa69c8931fc30 EFLAGS: 00000246
| RAX: 7fffffffffffffff RBX: ffff8ea9934a0040 RCX: 0000000000000000
| RDX: 0000000000000001 RSI: ffffffffbb4ab491 RDI: 00000000ffffffff
| RBP: ffffa69c8931fdc0 R08: 0000000000000001 R09: 0000000000000001
| R10: 00000000ffffffff R11: 00000000ffffffff R12: ffff8ea9934a0040
| R13: ffffffffbb792620 R14: 0000000000000108 R15: 0000000000000001
| get_signal+0xe56/0xe60 kernel/signal.c:2843
| arch_do_signal_or_restart+0x3f/0x780 arch/x86/kernel/signal.c:869
| exit_to_user_mode_loop kernel/entry/common.c:166 [inline]
| exit_to_user_mode_prepare+0x135/0x1a0 kernel/entry/common.c:201
| __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
| syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:294
| do_syscall_64+0x48/0x90 arch/x86/entry/common.c:86
| entry_SYSCALL_64_after_hwframe+0x64/0xce
| RIP: 0033:0x7fdcddc48549
| Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
| RSP: 002b:00007fdcddbb60f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
| RAX: 0000000000000001 RBX: 00007fdcddd62f88 RCX: 00007fdcddc48549
| RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007fdcddd62f8c
| RBP: 00007fdcddd62f80 R08: 000000000000001e R09: 0000000000000000
| R10: 0000000000000003 R11: 0000000000000246 R12: 00007fdcddd62f8c
| R13: 00007ffc4136118f R14: 0000000000000000 R15: 00007fdcddbb6640
| </TASK>
| irq event stamp: 128
| hardirqs last enabled at (127): [<ffffffffba9f7237>] irqentry_exit+0x37/0x90 kernel/entry/common.c:431
| hardirqs last disabled at (128): [<ffffffffba9faa5b>] __schedule+0x6cb/0xb20 kernel/sched/core.c:6393
| softirqs last enabled at (106): [<ffffffffbae0034f>] softirq_handle_end kernel/softirq.c:414 [inline]
| softirqs last enabled at (106): [<ffffffffbae0034f>] __do_softirq+0x34f/0x4d5 kernel/softirq.c:600
| softirqs last disabled at (99): [<ffffffffb9693821>] invoke_softirq kernel/softirq.c:445 [inline]
| softirqs last disabled at (99): [<ffffffffb9693821>] __irq_exit_rcu+0xb1/0x120 kernel/softirq.c:650
| ---[ end trace 0000000000000000 ]---
| BUG: kernel NULL pointer dereference, address: 0000000000000000
| #PF: supervisor instruction fetch in kernel mode
| #PF: error_code(0x0010) - not-present page
| PGD 8000000112e91067 P4D 8000000112e91067 PUD 114481067 PMD 0
| Oops: 0010 [#1] PREEMPT SMP PTI
| CPU: 1 PID: 13018 Comm: syz-executor.11 Tainted: G W 6.0.0-rc3-00017-g1472d7e42f41-dirty #65
| Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
| RIP: 0010:0x0
| Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
| RSP: 0018:ffffa69c8931fd18 EFLAGS: 00010293
| RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffb96be917
| RDX: ffff8ea9934a0040 RSI: 0000000000000000 RDI: ffff8ea99526f620
| RBP: ffff8ea9934a0040 R08: 0000000000000000 R09: 0000000000000000
| R10: 0000000000000001 R11: ffffffffb9cb7eaf R12: ffff8ea9934a08f0
| R13: ffff8ea992fc9cf8 R14: ffff8ea98c65dec0 R15: ffff8ea9934a0828
| FS: 0000000000000000(0000) GS:ffff8eacafc40000(0000) knlGS:0000000000000000
| CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
| CR2: ffffffffffffffd6 CR3: 000000011343a003 CR4: 0000000000770ee0
| DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
| DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
| PKRU: 55555554
| Call Trace:
| <TASK>
| task_work_run+0x73/0xc0 kernel/task_work.c:177
| exit_task_work include/linux/task_work.h:38 [inline]
| do_exit+0x459/0xf20 kernel/exit.c:795
| do_group_exit+0x3f/0xe0 kernel/exit.c:925
| get_signal+0xe04/0xe60 kernel/signal.c:2857
| arch_do_signal_or_restart+0x3f/0x780 arch/x86/kernel/signal.c:869
| exit_to_user_mode_loop kernel/entry/common.c:166 [inline]
| exit_to_user_mode_prepare+0x135/0x1a0 kernel/entry/common.c:201
| __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
| syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:294
| do_syscall_64+0x48/0x90 arch/x86/entry/common.c:86
| entry_SYSCALL_64_after_hwframe+0x64/0xce
| RIP: 0033:0x7fdcddc48549
| Code: Unable to access opcode bytes at RIP 0x7fdcddc4851f.
| RSP: 002b:00007fdcddbb60f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
| RAX: 0000000000000001 RBX: 00007fdcddd62f88 RCX: 00007fdcddc48549
| RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007fdcddd62f8c
| RBP: 00007fdcddd62f80 R08: 000000000000001e R09: 0000000000000000
| R10: 0000000000000003 R11: 0000000000000246 R12: 00007fdcddd62f8c
| R13: 00007ffc4136118f R14: 0000000000000000 R15: 00007fdcddbb6640
| </TASK>
| Modules linked in:
| CR2: 0000000000000000
| ---[ end trace 0000000000000000 ]---
| RIP: 0010:0x0
| Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
| RSP: 0018:ffffa69c8931fd18 EFLAGS: 00010293
| RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffb96be917
| RDX: ffff8ea9934a0040 RSI: 0000000000000000 RDI: ffff8ea99526f620
| RBP: ffff8ea9934a0040 R08: 0000000000000000 R09: 0000000000000000
| R10: 0000000000000001 R11: ffffffffb9cb7eaf R12: ffff8ea9934a08f0
| R13: ffff8ea992fc9cf8 R14: ffff8ea98c65dec0 R15: ffff8ea9934a0828
| FS: 0000000000000000(0000) GS:ffff8eacafc40000(0000) knlGS:0000000000000000
| CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
| CR2: ffffffffffffffd6 CR3: 000000011343a003 CR4: 0000000000770ee0
| DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
| DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
| PKRU: 55555554
| ----------------
| Code disassembly (best guess):
| 0: d3 25 df ff 83 e3 shll %cl,-0x1c7c0021(%rip) # 0xe383ffe5
| 6: 08 0f or %cl,(%rdi)
| 8: 84 f0 test %dh,%al
| a: 03 00 add (%rax),%eax
| c: 00 e8 add %ch,%al
| e: c5 25 df ff vpandn %ymm7,%ymm11,%ymm15
| 12: 48 f7 85 88 fe ff ff testq $0x100,-0x178(%rbp)
| 19: 00 01 00 00
| 1d: 0f 85 7e fc ff ff jne 0xfffffca1
| 23: 31 db xor %ebx,%ebx
| 25: e9 83 fc ff ff jmp 0xfffffcad
| * 2a: e8 a8 25 df ff call 0xffdf25d7 <-- trapping instruction
| 2f: e8 63 43 d3 ff call 0xffd34397
| 34: e9 d2 f1 ff ff jmp 0xfffff20b
| 39: e8 99 25 df ff call 0xffdf25d7
| 3e: 48 rex.W
| 3f: 85 .byte 0x85

So something isn't quite right yet. Unfortunately I don't have a good
reproducer. :-/

Thanks,
-- Marco

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