[BUG] perf/core: report a task hung issue in __perf_event_ctx_lock_double()

[liwei (GF)]

Hi peter,
The syzkaller reported a task hung issue, and it was on a qemu x86_64 machine with kernel 4.19.27.
I analysed and found that, the gctx got in __perf_event_ctx_lock_double and ctx are just equal.It is
caused by race between two concurrent sys_perf_event_open() calls where both try and move the same
pre-existing software group into a hardware context. In commit 321027c1fe77f8 ("perf/core: Fix
concurrent sys_perf_event_open() vs. 'move_group' race"), i found you have tried to solve this
problem before. I am afraid a only check can not avoid the race, should we use a lock here?

[ 1295.914975] INFO: task syz-executor.2:23733 blocked for more than 140 seconds.
[ 1295.921446]       Not tainted 4.19.27 #2
[ 1295.922994] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1295.925517] syz-executor.2  D27904 23733   2683 0x10000004
[ 1295.927009] Call Trace:
[ 1295.928737]  ? __schedule+0x755/0x1a80
[ 1295.931396]  ? __sched_text_start+0x8/0x8
[ 1295.936207]  ? do_raw_spin_unlock+0x54/0x220
[ 1295.937339]  schedule+0x7c/0x1a0
[ 1295.938256]  schedule_preempt_disabled+0x11/0x20
[ 1295.939493]  __mutex_lock+0x83b/0x1240
[ 1295.940548]  ? perf_event_ctx_lock_nested+0x1fd/0x440
[ 1295.952024]  ? mutex_lock_io_nested+0x10d0/0x10d0
[ 1295.953217]  ? perf_event_ctx_lock_nested+0x1fd/0x440
[ 1295.954488]  ? ftrace_ops_list_func+0x1c1/0x380
[ 1295.955611]  ? perf_trace_buf_alloc+0x200/0x200
[ 1295.956759]  ? ftrace_call+0x5/0x34
[ 1295.969703]  ? perf_event_ctx_lock_nested+0x1fd/0x440
[ 1295.971336]  ? perf_event_ctx_lock_nested+0x1fd/0x440
[ 1295.972778]  perf_event_ctx_lock_nested+0x1fd/0x440
[ 1295.974994]  ? perf_event_read_event+0x2a0/0x2a0
[ 1295.976346]  ? perf_event_release_kernel+0x94d/0xc70
[ 1295.977643]  ? perf_event_release_kernel+0x955/0xc70
[ 1295.978941]  perf_event_release_kernel+0x108/0xc70
[ 1295.980134]  ? ftrace_call+0x5/0x34
[ 1295.981086]  ? locks_remove_file+0x2b5/0x3e0
[ 1295.992160]  ? put_event+0x40/0x40
[ 1295.993186]  ? perf_event_release_kernel+0xc70/0xc70
[ 1295.994496]  perf_release+0x33/0x40
[ 1295.995494]  __fput+0x27f/0x7f0
[ 1295.996445]  task_work_run+0x136/0x1b0
[ 1295.997536]  exit_to_usermode_loop+0x1a7/0x1d0
[ 1295.998727]  do_syscall_64+0x461/0x580
[ 1295.999800]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 1296.001076] RIP: 0033:0x412387
[ 1296.001962] Code: Bad RIP value.
[ 1296.002768] RSP: 002b:00007ffde0b42b40 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
[ 1296.009717] RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000412387
[ 1296.011609] RDX: 0000000000000000 RSI: 0000000000741c60 RDI: 0000000000000004
[ 1296.013436] RBP: 00007ffde0b42bac R08: 00000000000ffd52 R09: 00000000000ffd52
[ 1296.035032] R10: 00007ffde0b42a80 R11: 0000000000000293 R12: 0000000000000001
[ 1296.039400] R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000002
[ 1296.052258] INFO: task syz-executor.2:23734 blocked for more than 140 seconds.
[ 1296.067589]       Not tainted 4.19.27 #2
[ 1296.068545] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1296.070573] syz-executor.2  D28432 23734   2683 0x10000004
[ 1296.072028] Call Trace:
[ 1296.072700]  ? __schedule+0x755/0x1a80
[ 1296.073747]  ? __sched_text_start+0x8/0x8
[ 1296.081141]  ? do_raw_spin_unlock+0x54/0x220
[ 1296.082784]  schedule+0x7c/0x1a0
[ 1296.084135]  schedule_preempt_disabled+0x11/0x20
[ 1296.085506]  __mutex_lock+0x83b/0x1240
[ 1296.086609]  ? __do_sys_perf_event_open+0xff5/0x2090
[ 1296.088051]  ? mutex_lock_io_nested+0x10d0/0x10d0
[ 1296.097169]  ? __do_sys_perf_event_open+0xff5/0x2090
[ 1296.098224]  ? ftrace_ops_list_func+0x1c1/0x380
[ 1296.099256]  ? perf_trace_buf_alloc+0x200/0x200
[ 1296.110608]  ? ftrace_call+0x5/0x34
[ 1296.111662]  ? __do_sys_perf_event_open+0xff5/0x2090
[ 1296.113844]  ? __do_sys_perf_event_open+0xff5/0x2090
[ 1296.115350]  __do_sys_perf_event_open+0xff5/0x2090
[ 1296.116812]  ? perf_event_set_output+0x480/0x480
[ 1296.118742]  ? rcu_read_lock_sched_held+0x107/0x120
[ 1296.120136]  ? syscall_trace_enter+0x285/0xb80
[ 1296.122451]  ? do_syscall_64+0x3e3/0x580
[ 1296.124165]  do_syscall_64+0xc8/0x580
[ 1296.125766]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 1296.128241] RIP: 0033:0x462eb9
[ 1296.130131] Code: Bad RIP value.
[ 1296.131104] RSP: 002b:00007f6024d51c58 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
[ 1296.132763] RAX: ffffffffffffffda RBX: 000000000073bf00 RCX: 0000000000462eb9
[ 1296.148678] RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000020000040
[ 1296.151821] RBP: 0000000000000005 R08: 0000000000000000 R09: 0000000000000000
[ 1296.156380] R10: 0000000000000008 R11: 0000000000000246 R12: 00007f6024d526bc
[ 1296.160438] R13: 00000000004c2df7 R14: 00000000006ffc10 R15: 00000000ffffffff
[ 1296.165410] 
[ 1296.165410] Showing all locks held in the system:
[ 1296.168411] 1 lock held by khungtaskd/54:
[ 1296.170580]  #0: 00000000d6c02832 (rcu_read_lock){....}, at: debug_show_all_locks+0x57/0x310
[ 1296.175315] 2 locks held by mingetty/2544:
[ 1296.177933]  #0: 00000000456410e4 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x80
[ 1296.182492]  #1: 000000008edb9b44 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1f7/0x1640
[ 1296.187036] 2 locks held by mingetty/2545:
[ 1296.189314]  #0: 000000009aa198a3 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x80
[ 1296.204916]  #1: 0000000042b7b2da (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1f7/0x1640
[ 1296.219194] 2 locks held by mingetty/2546:
[ 1296.221824]  #0: 00000000f6de8ca8 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x80
[ 1296.225920]  #1: 00000000d0591283 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1f7/0x1640
[ 1296.230199] 2 locks held by mingetty/2547:
[ 1296.232317]  #0: 000000007948d514 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x80
[ 1296.237411]  #1: 000000004c06529b (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1f7/0x1640
[ 1296.241735] 2 locks held by mingetty/2548:
[ 1296.243249]  #0: 00000000ffb56700 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x80
[ 1296.246098]  #1: 00000000b1156838 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1f7/0x1640
[ 1296.251057] 2 locks held by mingetty/2549:
[ 1296.252910]  #0: 0000000040841ffc (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x80
[ 1296.255309]  #1: 00000000729b4211 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1f7/0x1640
[ 1296.257465] 2 locks held by agetty/2550:
[ 1296.258726]  #0: 000000006bdfce31 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x80
[ 1296.264181]  #1: 000000000945aba2 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1f7/0x1640
[ 1296.270268] 1 lock held by syz-executor.2/23733:
[ 1296.272249]  #0: 00000000f7dcaa66 (&cpuctx_mutex){+.+.}, at: perf_event_ctx_lock_nested+0x1fd/0x440
[ 1296.274329] 2 locks held by syz-executor.2/23734:
[ 1296.275344]  #0: 00000000f7dcaa66 (&cpuctx_mutex){+.+.}, at: __do_sys_perf_event_open+0xfe8/0x2090
[ 1296.277915]  #1: 00000000f7dcaa66 (&cpuctx_mutex/1){+.+.}, at: __do_sys_perf_event_open+0xff5/0x2090
[ 1296.280048] 
[ 1296.280502] =============================================
[ 1296.280502] 

Thanks,
Wei Li