Date:   Tue, 29 Mar 2022 16:07:32 +0800
From:   Zhang Qiao <zhangqiao22@...wei.com>
To:     lkml <linux-kernel@...r.kernel.org>
CC:     <ebiederm@...ssion.com>
Subject: Question about kill a process group

hello everyone,

I got a hradlockup panic when run the ltp syscall testcases.

348439.713178] NMI watchdog: Watchdog detected hard LOCKUP on cpu 32
[348439.713236] irq event stamp: 0
[348439.713237] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
[348439.713238] hardirqs last disabled at (0): [<ffffffff87cd1ea5>] copy_process+0x7f5/0x2160
[348439.713239] softirqs last  enabled at (0): [<ffffffff87cd1ea5>] copy_process+0x7f5/0x2160
[348439.713240] softirqs last disabled at (0): [<0000000000000000>] 0x0
[348439.713241] CPU: 32 PID: 1151212 Comm: fork12 Kdump: loaded Tainted: G S                5.10.0+ #1
[348439.713242] Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 3.35 10/20/2016
[348439.713243] RIP: 0010:queued_write_lock_slowpath+0x4d/0x80
[348439.713245] RSP: 0018:ffffa3a6bed4fe60 EFLAGS: 00000006
[348439.713246] RAX: 0000000000000500 RBX: ffffffff892060c0 RCX: 00000000000000ff
[348439.713247] RDX: 0000000000000500 RSI: 0000000000000100 RDI: ffffffff892060c0
[348439.713248] RBP: ffffffff892060c4 R08: 0000000000000001 R09: 0000000000000000
[348439.713249] R10: ffffa3a6bed4fde8 R11: 0000000000000000 R12: ffff96dfd3b68001
[348439.713250] R13: ffff96dfd3b68000 R14: ffff96dfd3b68c38 R15: ffff96e2cf1f51c0
[348439.713251] FS:  0000000000000000(0000) GS:ffff96edbc200000(0000) knlGS:0000000000000000
[348439.713252] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[348439.713253] CR2: 0000000000416ea0 CR3: 0000002d91812004 CR4: 00000000001706e0
[348439.713254] Call Trace:
[348439.713255]  do_raw_write_lock+0xa9/0xb0
[348439.713256]  _raw_write_lock_irq+0x5a/0x70
[348439.713256]  do_exit+0x429/0xd00
[348439.713257]  do_group_exit+0x39/0xb0
[348439.713258]  __x64_sys_exit_group+0x14/0x20
[348439.713259]  do_syscall_64+0x33/0x40
[348439.713260]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[348439.713260] RIP: 0033:0x7f59295a7066
[348439.713261] Code: Unable to access opcode bytes at RIP 0x7f59295a703c.
[348439.713262] RSP: 002b:00007fff0afeac38 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
[348439.713264] RAX: ffffffffffffffda RBX: 00007f5929694530 RCX: 00007f59295a7066
[348439.713265] RDX: 0000000000000002 RSI: 000000000000003c RDI: 0000000000000002
[348439.713266] RBP: 0000000000000002 R08: 00000000000000e7 R09: ffffffffffffff80
[348439.713267] R10: 0000000000000002 R11: 0000000000000246 R12: 00007f5929694530
[348439.713268] R13: 0000000000000001 R14: 00007f5929697f68 R15: 0000000000000000
[348439.713269] Kernel panic - not syncing: Hard LOCKUP
[348439.713270] CPU: 32 PID: 1151212 Comm: fork12 Kdump: loaded Tainted: G S                5.10.0+ #1
[348439.713272] Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 3.35 10/20/2016
[348439.713272] Call Trace:
[348439.713273]  <NMI>
[348439.713274]  dump_stack+0x77/0x97
[348439.713275]  panic+0x10c/0x2fb
[348439.713275]  nmi_panic+0x35/0x40
[348439.713276]  watchdog_hardlockup_check+0xeb/0x110
[348439.713277]  __perf_event_overflow+0x52/0xf0
[348439.713278]  handle_pmi_common+0x21a/0x320
[348439.713286]  intel_pmu_handle_irq+0xc9/0x1b0
[348439.713287]  perf_event_nmi_handler+0x24/0x40
[348439.713288]  nmi_handle+0xc3/0x2a0
[348439.713289]  default_do_nmi+0x49/0xf0
[348439.713289]  exc_nmi+0x146/0x160
[348439.713290]  end_repeat_nmi+0x16/0x55
[348439.713291] RIP: 0010:queued_write_lock_slowpath+0x4d/0x80
[348439.713293] RSP: 0018:ffffa3a6bed4fe60 EFLAGS: 00000006
[348439.713295] RAX: 0000000000000500 RBX: ffffffff892060c0 RCX: 00000000000000ff
[348439.713296] RDX: 0000000000000500 RSI: 0000000000000100 RDI: ffffffff892060c0
[348439.713296] RBP: ffffffff892060c4 R08: 0000000000000001 R09: 0000000000000000
[348439.713297] R10: ffffa3a6bed4fde8 R11: 0000000000000000 R12: ffff96dfd3b68001
[348439.713298] R13: ffff96dfd3b68000 R14: ffff96dfd3b68c38 R15: ffff96e2cf1f51c0
[348439.713300]  </NMI>
[348439.713301]  do_raw_write_lock+0xa9/0xb0
[348439.713302]  _raw_write_lock_irq+0x5a/0x70
[348439.713303]  do_exit+0x429/0xd00
[348439.713303]  do_group_exit+0x39/0xb0
[348439.713304]  __x64_sys_exit_group+0x14/0x20
[348439.713305]  do_syscall_64+0x33/0x40
[348439.713306]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[348439.713307] RIP: 0033:0x7f59295a7066
[348439.713308] Code: Unable to access opcode bytes at RIP 0x7f59295a703c.


when analyzing vmcore, i notice lots of fork12 processes are waiting for tasklist read lock or write
lock (see the attachment file all_cpu_stacks.log)，and every fork12 process(belongs to the same
process group) call kill(0, SIGQUIT) in their signal handler()[1], it will traverse all the processes in the
same process group and send signal to them one by one, which is a very time-costly work and hold tasklist
read lock long time. At the same time, other processes will exit after receive signal, they try to get
the tasklist write lock at exit_notify().

[1] fork12 testcase: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/fork/fork12.c

some processes call kill(0, SIGQUIT), wait for tasklist read lock:

 #5 [ffff972a9b16fd78] native_queued_spin_lock_slowpath at ffffffff9931ed47
 #6 [ffff972a9b16fd78] queued_read_lock_slowpath at ffffffff99320a58
 #7 [ffff972a9b16fd90] do_wait at ffffffff992bc17d
 #8 [ffff972a9b16fdd0] kernel_wait4 at ffffffff992bd88d
 #9 [ffff972a9b16fe58] __do_sys_wait4 at ffffffff992bd9e5
#10 [ffff972a9b16ff30] do_syscall_64 at ffffffff9920432d
#11 [ffff972a9b16ff50] entry_SYSCALL_64_after_hwframe at ffffffff99c000ad

As the same time, some processes are exiting, wait for tasklist write lock:

 #5 [ffff972aa49a7e60] native_queued_spin_lock_slowpath at ffffffff9931ecb0
 #6 [ffff972aa49a7e60] queued_write_lock_slowpath at ffffffff993209e4
 #7 [ffff972aa49a7e78] do_raw_write_lock at ffffffff99320834
 #8 [ffff972aa49a7e88] do_exit at ffffffff992bcd78
 #9 [ffff972aa49a7f00] do_group_exit at ffffffff992bd719
#10 [ffff972aa49a7f28] __x64_sys_exit_group at ffffffff992bd7a4
#11 [ffff972aa49a7f30] do_syscall_64 at ffffffff9920432d
#12 [ffff972aa49a7f50] entry_SYSCALL_64_after_hwframe at ffffffff99c000ad

In this scenario,there are lots of process are waiting for tasklist read lock or the tasklist
write lock, so they will queue. if the wait queue is long enough, it might cause a hardlockup issue when a
process wait for taking the write lock at exit_notify().

I tried to solve this problem by avoiding traversing the process group multiple times when kill(0, xxxx)
is called multiple times form the same process group, but it doesn't look like a good solution.

Is there any good idea for fixing this problem ?

Thanks!

Qiao
.

View attachment "all_cpu_stack.log" of type "text/plain" (113592 bytes)

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