[bug report] WARNINGs in rb_check_pages() and rb_handle_head_page()

[Zheng Yejian]

Hi, steve

I happened to get two WARNINGs [1] [2] at same time when testing v5.10 with
testcase 'func_profiler.tc':
Link: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/ftrace/test.d/ftrace/func_profiler.tc

It seems a data race between ring_buffer writing and integrity checking.
That is, head_page is moving when buffer is full and RB_FLAG is updating,
however at same time RB_FLAG was cleared when doing integrity check:
  rb_check_pages()            rb_handle_head_page():
  --------                    --------
  rb_head_page_deactivate()
                              rb_head_page_set_normal()
  rb_head_page_activate()

Mainline kernel seems have this problem as well, see the constructed
testcase 'repro.sh' [3] and reproduction log [4].

Integrity checking of ring_buffer on closing "trace" file seems not a good
point, do you have any idea, steve?

1:
One WARNING happened at
Link: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/trace/ring_buffer.c?h=linux-5.10.y#n1492
  Call Trace:
   rb_check_pages
   ring_buffer_read_finish
   tracing_release

2:
The other WARNING happened at
Link: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/trace/ring_buffer.c?h=linux-5.10.y#n2507
  Call Trace:
   rb_handle_head_page
   rb_move_tail
   __rb_reserve_next
   rb_reserve_next_event
   ring_buffer_lock_reserve
   __trace_buffer_lock_reserve
   trace_function
   function_trace_call

3:
``` read_trace.sh
  while true;
  do
    # the "trace" file is closed after read
    head -1 /sys/kernel/tracing/trace > /dev/null
  done
```
``` repro.sh
  # function tracer will writing enough data into ring_buffer
  echo function > /sys/kernel/tracing/current_tracer
  ./read_trace.sh &
  ./read_trace.sh &
  ./read_trace.sh &
  ./read_trace.sh &
  ./read_trace.sh &
  ./read_trace.sh &
  ./read_trace.sh &
  ./read_trace.sh &
```

4:
------------[ cut here ]------------
WARNING: CPU: 9 PID: 62 at kernel/trace/ring_buffer.c:2653 rb_move_tail+0x450/0x470
Modules linked in:
CPU: 9 PID: 62 Comm: ksoftirqd/9 Tainted: G        W          6.2.0-rc6+ #261
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
RIP: 0010:rb_move_tail+0x450/0x470
Code: ff ff 4c 89 c8 f0 4d 0f b1 02 48 89 c2 48 83 e2 fc 49 39 d0 75 24 83 e0 03 83 f8 02 0f 84 e1 fb ff ff 48 8b 57 10 f0 ff 42 08 <0f> 0b 83 f8 02 0f 84 ce fb ff ff e9 db
RSP: 0018:ffffb5564089bd00 EFLAGS: 00000203
RAX: 0000000000000000 RBX: ffff9db385a2bf81 RCX: ffffb5564089bd18
RDX: ffff9db281110100 RSI: 0000000000000fe4 RDI: ffff9db380145400
RBP: ffff9db385a2bf80 R08: ffff9db385a2bfc0 R09: ffff9db385a2bfc2
R10: ffff9db385a6c000 R11: ffff9db385a2bf80 R12: 0000000000000000
R13: 00000000000003e8 R14: ffff9db281110100 R15: ffffffffbb006108
FS:  0000000000000000(0000) GS:ffff9db3bdcc0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005602323024c8 CR3: 0000000022e0c000 CR4: 00000000000006e0
Call Trace:
 <TASK>
 ring_buffer_lock_reserve+0x136/0x360
 ? __do_softirq+0x287/0x2df
 ? __pfx_rcu_softirq_qs+0x10/0x10
 trace_function+0x21/0x110
 ? __pfx_rcu_softirq_qs+0x10/0x10
 ? __do_softirq+0x287/0x2df
 function_trace_call+0xf6/0x120
 0xffffffffc038f097
 ? rcu_softirq_qs+0x5/0x140
 rcu_softirq_qs+0x5/0x140
 __do_softirq+0x287/0x2df
 run_ksoftirqd+0x2a/0x30
 smpboot_thread_fn+0x188/0x220
 ? __pfx_smpboot_thread_fn+0x10/0x10
 kthread+0xe7/0x110
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x2c/0x50
 </TASK>
---[ end trace 0000000000000000 ]---