INFO: task can't die in perf_event_free

INFO: task can't die in perf_event_free_task
Status: upstream: reported syz repro on 2020/11/19 15:42
Reported-by: syzbot+f02b92479b7065807a2a@syzkaller.appspotmail.com
First crash: 156d, last: 156d

Cause bisection: introduced by (bisect log) [no-op commit]:
commit ab2dd173330a3f07142e68cd65682205036cd00f
Author: Andy Lutomirski <luto@kernel.org>
Date: Wed Aug 26 17:00:45 2020 +0000

selftests/x86/fsgsbase: Reap a forgotten child

Crash: INFO: task hung in perf_event_free_task (log)
Repro: syz .config

Sample crash report:

INFO: task syz-executor.0:26152 can't die for more than 143 seconds.
task:syz-executor.0  state:D stack:28544 pid:26152 ppid:  8500 flags:0x00004004
Call Trace:
 context_switch kernel/sched/core.c:4269 [inline]
 __schedule+0x890/0x2030 kernel/sched/core.c:5019
 schedule+0xcf/0x270 kernel/sched/core.c:5098
 perf_event_free_task+0x514/0x6b0 kernel/events/core.c:12605
 copy_process+0x48e0/0x6f90 kernel/fork.c:2360
 kernel_clone+0xe7/0xab0 kernel/fork.c:2462
 __do_sys_clone+0xc8/0x110 kernel/fork.c:2579
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45deb9
Code: Unable to access opcode bytes at RIP 0x45de8f.
RSP: 002b:00007ffb605e6c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000002040 RCX: 000000000045deb9
RDX: 9999999999999999 RSI: 0000000000000000 RDI: 0000000000000100
RBP: 000000000118bf70 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007fff8d97524f R14: 00007ffb605e79c0 R15: 000000000118bf2c
INFO: task syz-executor.0:26152 blocked for more than 143 seconds.
      Not tainted 5.10.0-rc3-next-20201113-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.0  state:D stack:28544 pid:26152 ppid:  8500 flags:0x00004004
Call Trace:
 context_switch kernel/sched/core.c:4269 [inline]
 __schedule+0x890/0x2030 kernel/sched/core.c:5019
 schedule+0xcf/0x270 kernel/sched/core.c:5098
 perf_event_free_task+0x514/0x6b0 kernel/events/core.c:12605
 copy_process+0x48e0/0x6f90 kernel/fork.c:2360
 kernel_clone+0xe7/0xab0 kernel/fork.c:2462
 __do_sys_clone+0xc8/0x110 kernel/fork.c:2579
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45deb9
Code: Unable to access opcode bytes at RIP 0x45de8f.
RSP: 002b:00007ffb605e6c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000002040 RCX: 000000000045deb9
RDX: 9999999999999999 RSI: 0000000000000000 RDI: 0000000000000100
RBP: 000000000118bf70 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007fff8d97524f R14: 00007ffb605e79c0 R15: 000000000118bf2c

Showing all locks held in the system:
1 lock held by khungtaskd/1567:
 #0: ffffffff8b339ce0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6252
1 lock held by in:imklog/8178:
 #0: ffff88801c937c70 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:932

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 1567 Comm: khungtaskd Not tainted 5.10.0-rc3-next-20201113-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 nmi_cpu_backtrace.cold+0x44/0xd7 lib/nmi_backtrace.c:105
 nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:147 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:253 [inline]
 watchdog+0xd89/0xf30 kernel/hung_task.c:338
 kthread+0x3af/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
NMI backtrace for cpu 1 skipped: idling at acpi_safe_halt drivers/acpi/processor_idle.c:111 [inline]
NMI backtrace for cpu 1 skipped: idling at acpi_idle_do_entry+0x1c9/0x250 drivers/acpi/processor_idle.c:517

Crashes (1):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Title
ci-upstream-linux-next-kasan-gce-root	2020/11/15 15:35	linux-next	92edc4ae	1bf9a662	.config	log	report	syz