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From: Jens Axboe <[email protected]>
To: "Eric W. Biederman" <[email protected]>
Cc: [email protected], [email protected],
	[email protected], [email protected], [email protected]
Subject: Re: [PATCH 0/2] Don't show PF_IO_WORKER in /proc/<pid>/task/
Date: Thu, 25 Mar 2021 13:40:34 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 3/25/21 1:33 PM, Eric W. Biederman wrote:
> Jens Axboe <[email protected]> writes:
> 
>> Hi,
>>
>> Stefan reports that attaching to a task with io_uring will leave gdb
>> very confused and just repeatedly attempting to attach to the IO threads,
>> even though it receives an -EPERM every time. This patchset proposes to
>> skip PF_IO_WORKER threads as same_thread_group(), except for accounting
>> purposes which we still desire.
>>
>> We also skip listing the IO threads in /proc/<pid>/task/ so that gdb
>> doesn't think it should stop and attach to them. This makes us consistent
>> with earlier kernels, where these async threads were not related to the
>> ring owning task, and hence gdb (and others) ignored them anyway.
>>
>> Seems to me that this is the right approach, but open to comments on if
>> others agree with this. Oleg, I did see your messages as well on SIGSTOP,
>> and as was discussed with Eric as well, this is something we most
>> certainly can revisit. I do think that the visibility of these threads
>> is a separate issue. Even with SIGSTOP implemented (which I did try as
>> well), we're never going to allow ptrace attach and hence gdb would still
>> be broken. Hence I'd rather treat them as separate issues to attack.
> 
> A quick skim shows that these threads are not showing up anywhere in
> proc which appears to be a problem, as it hides them from top.
> 
> Sysadmins need the ability to dig into a system and find out where all
> their cpu usage or io's have gone when there is a problem.  I general I
> think this argues that these threads should show up as threads of the
> process so I am not even certain this is the right fix to deal with gdb.

That's a good point, overall hiding was not really what I desired, just
getting them out of gdb's hands. And arguably it _is_ a gdb bug, but...

-- 
Jens Axboe


  parent reply	other threads:[~2021-03-25 19:41 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-25 16:43 [PATCH 0/2] Don't show PF_IO_WORKER in /proc/<pid>/task/ Jens Axboe
2021-03-25 16:43 ` [PATCH 1/2] kernel: don't include PF_IO_WORKERs as part of same_thread_group() Jens Axboe
2021-03-25 16:43 ` [PATCH 2/2] proc: don't show PF_IO_WORKER threads as threads in /proc/<pid>/task/ Jens Axboe
2021-03-25 19:33 ` [PATCH 0/2] Don't show PF_IO_WORKER " Eric W. Biederman
2021-03-25 19:38   ` Linus Torvalds
2021-03-25 19:40     ` Jens Axboe
2021-03-25 19:42     ` Linus Torvalds
2021-03-25 19:46       ` Jens Axboe
2021-03-25 20:21         ` Eric W. Biederman
2021-03-25 20:40           ` Oleg Nesterov
2021-03-25 20:43             ` Jens Axboe
2021-03-25 20:48             ` Eric W. Biederman
2021-03-25 20:42           ` Jens Axboe
2021-03-25 20:12       ` Linus Torvalds
2021-03-25 20:40         ` Jens Axboe
2021-03-25 21:44           ` Jens Axboe
2021-03-25 21:57             ` Stefan Metzmacher
2021-03-26  0:11               ` Jens Axboe
2021-03-26 11:59                 ` Stefan Metzmacher
2021-04-01 14:40                   ` Stefan Metzmacher
2021-03-25 22:37             ` Linus Torvalds
2021-03-26  0:08               ` Jens Axboe
2021-03-25 20:43         ` Eric W. Biederman
2021-03-25 21:50           ` Jens Axboe
2021-03-25 20:44         ` Oleg Nesterov
2021-03-25 20:55           ` Eric W. Biederman
2021-03-25 21:20             ` Stefan Metzmacher
2021-03-25 21:48               ` Stefan Metzmacher
2021-03-25 19:40   ` Jens Axboe [this message]
2021-03-25 20:32     ` Oleg Nesterov

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