From: Junyeong Jeong <esrse.jeong@gmail.com>
To: Greg KH <greg@kroah.com>
Cc: kernelnewbies@kernelnewbies.org
Subject: Re: /sys/devices/system/cpu/possible is immutable?
Date: Fri, 19 Mar 2021 00:45:07 +0900 [thread overview]
Message-ID: <877dm41n0k.fsf@gmail.com> (raw)
In-Reply-To: <YFNuuIOxA1CCY8Uq@kroah.com>
>
> That sysfs value itself will not change for the single system while the
> kernel is running, but your program could be moved from a system with
> one value for that file, to another system with a different value while
> it is running without knowing that you were migrated.
>
Running process migration to another system? Wow, I never knew that.
If migration happens between the time of reading
/sys/devices/system/cpu/possible and the time of calling
`bpf_lookup_elem`, TOCTOU(Time of check to Time of Use) problem would
arise. HaHa.
> So be careful here, and use the "normal" api to deal with cpu values and
> numbers, never assume that once you start, that the number of cpus your
> program has access to will not change.
Thank you Kroah-Hartman for your advice.
regards,
Junyeong
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prev parent reply other threads:[~2021-03-18 15:48 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 14:10 /sys/devices/system/cpu/possible is immutable? Junyeong Jeong
2021-03-18 15:16 ` Greg KH
2021-03-18 15:45 ` Junyeong Jeong [this message]
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