Re: [PATCH v2] tracing: Remove definition of trace_*_rcuidle()

[Guenter Roeck <linux@roeck-us.net>]

On 12/3/24 12:55, Steven Rostedt wrote:
> 
> [ Adding MIPS maintainers ]
> 
> On Tue, 3 Dec 2024 12:39:08 -0800
> Guenter Roeck <linux@roeck-us.net> wrote:
> 
>> Hi Steven,
>>
>> On Thu, Oct 03, 2024 at 06:16:29PM -0400, Steven Rostedt wrote:
>>> From: Steven Rostedt <rostedt@goodmis.org>
>>>
>>> The trace_*_rcuidle() variant of a tracepoint was to handle places where a
>>> tracepoint was located but RCU was not "watching". All those locations
>>> have been removed, and RCU should be watching where all tracepoints are
>>> located. We can now remove the trace_*_rcuidle() variant.
>>>
>>> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
>>> ---
>>
>> This patch triggers backtraces with mips qemu emulations.
>>
>> WARNING: CPU: 0 PID: 0 at include/trace/events/preemptirq.h:36 handle_int+0x128/0x178
>> RCU not watching for tracepoint
>> ...
>> Call Trace:
>> [<ffffffff8012a89c>] show_stack+0x64/0x158
>> [<ffffffff8011e998>] dump_stack_lvl+0xb4/0x128
>> [<ffffffff801550f4>] __warn+0xa4/0x1f8
>> [<ffffffff80155328>] warn_slowpath_fmt+0xe0/0x1d0
>> [<ffffffff801233e8>] handle_int+0x128/0x178
>> [<ffffffff80f25ff8>] r4k_wait+0x30/0x40
>> [<ffffffff80f26448>] default_idle_call+0xa0/0x330
>> [<ffffffff801b6ccc>] do_idle+0xe4/0x1b8
>> [<ffffffff801b71c4>] cpu_startup_entry+0x34/0x48
>> [<ffffffff80f2689c>] kernel_init+0x0/0x110
>>
>> WARNING: CPU: 0 PID: 0 at include/trace/events/preemptirq.h:40 trace_hardirqs_on+0x184/0x240
>> RCU not watching for tracepoint
>> ...
>> Call Trace:
>> [<ffffffff8012a89c>] show_stack+0x64/0x158
>> [<ffffffff8011e998>] dump_stack_lvl+0xb4/0x128
>> [<ffffffff801550f4>] __warn+0xa4/0x1f8
>> [<ffffffff80155328>] warn_slowpath_fmt+0xe0/0x1d0
>> [<ffffffff8028fb74>] trace_hardirqs_on+0x184/0x240
>> [<ffffffff80123030>] restore_partial+0x6c/0x13c
>>
>> Bisect log is attached.
> 
> I'm guessing MIPS needs to implement something like what arm64 did with:
> 
>   7cd1ea1010acb ("arm64: entry: fix non-NMI kernel<->kernel transitions")
> 
> Because we do not want to bring back the trace_*_rcuidle() crap.
> 

Hmm. If you say so. Note that powerpc has the same or a similar problem.

[    0.142039][    T0] RCU not watching for tracepoint
[    0.142488][    T0]
[    0.142659][    T0] =============================
[    0.142755][    T0] WARNING: suspicious RCU usage
[    0.142914][    T0] 6.13.0-rc1-00058-ge75ce84aa5d3 #1 Not tainted
[    0.143082][    T0] -----------------------------
[    0.143178][    T0] kernel/notifier.c:586 notify_die called but RCU thinks we're quiescent!


[    0.152733][    T0] RCU not watching for tracepoint
[    0.152770][    T0]
[    0.152995][    T0] =============================
[    0.153092][    T0] WARNING: suspicious RCU usage
[    0.153187][    T0] 6.13.0-rc1-00058-ge75ce84aa5d3 #1 Not tainted
[    0.153301][    T0] -----------------------------
[    0.153394][    T0] include/linux/rcupdate.h:850 rcu_read_lock() used illegally while idle!

[    0.165396][    T0] RCU not watching for tracepoint
[    0.165540][    T0]
[    0.165712][    T0] =============================
[    0.165811][    T0] WARNING: suspicious RCU usage
[    0.165909][    T0] 6.13.0-rc1-00058-ge75ce84aa5d3 #1 Not tainted
[    0.166026][    T0] -----------------------------
[    0.166122][    T0] include/linux/rcupdate.h:878 rcu_read_unlock() used illegally while idle!

and many more.

Guenter