由于 fanotify 代码中阻塞的任务,系统挂起

Issue

在控制台上带有多个阻塞任务警告的定期系统挂起：

kernel: INFO: task fsnotify_mark:159 blocked for more than 120 seconds.
kernel: INFO: task tail:52498 blocked for more than 120 seconds.
kernel: INFO: task systemd:1 blocked for more than 120 seconds.

系统可能部分或完全没有响应。任何用户空间任务都可能会阻塞。更具体地说，我们通常看到 systemd 或 fsnotify_mark 进程卡在 D-状态。大多数阻塞的任务都有类似于以下的堆栈追踪。请注意，每个都包含一些 fsnotify 或 fanotify 函数。

PID: 57101  TASK: ffff8800897a3980  CPU: 0   COMMAND: "java"
#0 [ffff880425c37ab8] __schedule at ffffffff8163b5bd
#1 [ffff880425c37b20] schedule at ffffffff8163bc59
#2 [ffff880425c37b30] fanotify_handle_event at ffffffff81226808
#3 [ffff880425c37b98] fsnotify at ffffffff81222510
#4 [ffff880425c37c88] security_file_open at ffffffff812868f6
#5 [ffff880425c37ca8] do_dentry_open at ffffffff811dc61e
#6 [ffff880425c37cf0] vfs_open at ffffffff811dc939
#7 [ffff880425c37d00] do_last at ffffffff811ebf2d
#8 [ffff880425c37db0] path_openat at ffffffff811eec92
#9 [ffff880425c37e48] do_filp_open at ffffffff811f045b
#10 [ffff880425c37f18] do_sys_open at ffffffff811dde03
#11 [ffff880425c37f70] sys_open at ffffffff811ddf1e
#12 [ffff880425c37f80] system_call_fastpath at ffffffff81646c49
RIP: 00007f76bdfea9cd  RSP: 00007f76990d8230  RFLAGS: 00010202
RAX: 0000000000000002  RBX: ffffffff81646c49  RCX: 0000000000000001
RDX: 00000000000001b6  RSI: 0000000000000042  RDI: 00007f76381f6730
RBP: 00007f76990d8270   R8: 00007f76381f6730   R9: 0000000000000035
R10: 0000000000000004  R11: 0000000000000293  R12: ffffffff811ddf1e
R13: ffff880425c37f78  R14: 0000000000000042  R15: 00000000000001b6
ORIG_RAX: 0000000000000002  CS: 0033  SS: 002b

PID: 1      TASK: ffff880428590000  CPU: 3   COMMAND: "systemd"
#0 [ffff88042859bc70] __schedule at ffffffff8163b5bd
#1 [ffff88042859bcd8] schedule at ffffffff8163bc59
#2 [ffff88042859bce8] schedule_timeout at ffffffff81639949
#3 [ffff88042859bd98] wait_for_completion at ffffffff8163c026
#4 [ffff88042859bdf8] __synchronize_srcu at ffffffff810ab6c6
#5 [ffff88042859be78] fsnotify_destroy_group at ffffffff8122345e
#6 [ffff88042859be90] inotify_release at ffffffff812256e2
#7 [ffff88042859bea8] __fput at ffffffff811e0949
#8 [ffff88042859bef0] ____fput at ffffffff811e0c0e
#9 [ffff88042859bf00] task_work_run at ffffffff810a2317
#10 [ffff88042859bf30] do_notify_resume at ffffffff81014b12
#11 [ffff88042859bf50] int_signal at ffffffff81646efd
RIP: 00007f09a90e228d  RSP: 00007fff140709d0  RFLAGS: 00000293
RAX: 0000000000000000  RBX: 000000000000001b  RCX: ffffffffffffffff
RDX: 00007f09a90cd7b8  RSI: 0000000000000000  RDI: 000000000000001b
RBP: 00007f09aa5cd710   R8: 0000000000000001   R9: 00007f09aa6d5945
R10: 0000000000000000  R11: 0000000000000293  R12: 0000000000000000
R13: 00007f09ac3dd870  R14: 00007f09ac53e680  R15: 0000000000000000
ORIG_RAX: 0000000000000003  CS: 0033  SS: 002b