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From: Stefan Metzmacher <>
To: Steven Rostedt <>
Cc: Ingo Molnar <>,,
	io-uring <>,
	"" <>
Subject: Re: sched_waking vs. set_event_pid crash (Re: Tracing busy processes/threads freezes/stalls the whole machine)
Date: Fri, 23 Jul 2021 13:53:41 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210723072906.4f4e7bd5@gandalf.local.home>

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Hi Steve,

>>> Assuming this does fix your issue, I sent out a real patch with the
>>> explanation of what happened in the change log, so that you can see why
>>> that change was your issue.  
>> Yes, it does the trick, thanks very much!
> Can I get a "Tested-by" from you?


Can you check if the static_key_disable() and static_key_enable()
calls are correctly ordered compared to rcu_assign_pointer()
and explain why they are, as I not really understand that it's different
from tracepoint_update_call vs. rcu_assign_pointer

>> Now I can finally use:
>> trace-cmd record -e all -P $(pidof io_uring-cp-forever)
>> But that doesn't include the iou-wrk-* threads
>> and the '-c' option seems to only work with forking.
> Have you tried it? It should work for threads as well. It hooks to the
> sched_process_fork tracepoint, which should be triggered even when a new
> thread is created.
> Or do you mean that you want that process and all its threads too that are
> already running? I could probably have it try to add it via the /proc file
> system in that case.
> Can you start the task via trace-cmd?
>   trace-cmd record -e all -F -c io_uring-cp-forever ...

I think that would work, but I typically want to analyze a process
that is already running.

>> Is there a way to specify "trace *all* threads of the given pid"?
>> (Note the threads are comming and going, so it's not possible to
>> specifiy -P more than once)
> Right, although, you could append tasks manually to the set_event_pid file
> from another terminal after starting trace-cmd. Once a pid is added to that
> file, all children it makes will also be added. That could be a work around
> until we have trace-cmd do it.

Sure, but it will always be racy.

With children, does new threads also count as children or only fork() children?

> Care to write a bugzilla report for this feature?

I may do later...


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  reply	other threads:[~2021-07-23 11:54 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2021-05-04 12:26 ` Tracing busy processes/threads freezes/stalls the whole machine Stefan Metzmacher
     [not found] ` <20210504092404.6b12aba4@gandalf.local.home>
     [not found]   ` <>
     [not found]     ` <20210504093550.5719d4bd@gandalf.local.home>
     [not found]       ` <>
     [not found]         ` <>
     [not found]           ` <>
2021-07-22 22:43             ` sched_waking vs. set_event_pid crash (Re: Tracing busy processes/threads freezes/stalls the whole machine) Stefan Metzmacher
2021-07-23  1:41               ` Steven Rostedt
2021-07-23  2:51               ` Steven Rostedt
2021-07-23 10:35                 ` Stefan Metzmacher
2021-07-23 11:29                   ` Steven Rostedt
2021-07-23 11:53                     ` Stefan Metzmacher [this message]
2021-07-23 12:41                       ` Steven Rostedt

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