From: Daniel Jordan <daniel.m.jordan-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
To: Alexey Klimov <aklimov-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
yury.norov-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org,
Joshua Baker <jobaker-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
audralmitchel-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
arnd-r2nGTMty4D4@public.gmane.org,
gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org,
rafael-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
Qais Yousef <qais.yousef-5wv7dgnIgG8@public.gmane.org>,
hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org,
Alexey Klimov
<klimov.linux-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH v2] cpu/hotplug: wait for cpuset_hotplug_work to finish on cpu onlining
Date: Thu, 18 Mar 2021 15:12:25 -0400 [thread overview]
Message-ID: <87a6r0uvhi.fsf@oracle.com> (raw)
In-Reply-To: <CAFBcO+99Ax5MuOtzNx=NrmnUN=+913Sc-DV83ObOi01A=kkN3w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
Alexey Klimov <aklimov-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> writes:
> The first section of comment seems problematic to me with regards to such move:
>
> * As this needs to hold the cpu maps lock it's impossible
> * to call device_offline() because that ends up calling
> * cpu_down() which takes cpu maps lock. cpu maps lock
> * needs to be held as this might race against in kernel
> * abusers of the hotplug machinery (thermal management).
>
> Cpu maps lock is released in cpu_maps_update_done() hence we will move
> dev->offline out of cpu maps lock. Maybe I misunderstood the comment
> and it relates to calling cpu_down_maps_locked() under lock to avoid
> race?
Yes, that's what I take from the comment, the cpu maps lock protects
against racing hotplug operations.
WARNING: multiple messages have this Message-ID (diff)
From: Daniel Jordan <daniel.m.jordan@oracle.com>
To: Alexey Klimov <aklimov@redhat.com>
Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
yury.norov@gmail.com, tglx@linutronix.de,
Joshua Baker <jobaker@redhat.com>,
audralmitchel@gmail.com, arnd@arndb.de,
gregkh@linuxfoundation.org, rafael@kernel.org, tj@kernel.org,
Qais Yousef <qais.yousef@arm.com>,
hannes@cmpxchg.org, Alexey Klimov <klimov.linux@gmail.com>
Subject: Re: [PATCH v2] cpu/hotplug: wait for cpuset_hotplug_work to finish on cpu onlining
Date: Thu, 18 Mar 2021 15:12:25 -0400 [thread overview]
Message-ID: <87a6r0uvhi.fsf@oracle.com> (raw)
In-Reply-To: <CAFBcO+99Ax5MuOtzNx=NrmnUN=+913Sc-DV83ObOi01A=kkN3w@mail.gmail.com>
Alexey Klimov <aklimov@redhat.com> writes:
> The first section of comment seems problematic to me with regards to such move:
>
> * As this needs to hold the cpu maps lock it's impossible
> * to call device_offline() because that ends up calling
> * cpu_down() which takes cpu maps lock. cpu maps lock
> * needs to be held as this might race against in kernel
> * abusers of the hotplug machinery (thermal management).
>
> Cpu maps lock is released in cpu_maps_update_done() hence we will move
> dev->offline out of cpu maps lock. Maybe I misunderstood the comment
> and it relates to calling cpu_down_maps_locked() under lock to avoid
> race?
Yes, that's what I take from the comment, the cpu maps lock protects
against racing hotplug operations.
next prev parent reply other threads:[~2021-03-18 19:12 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-12 0:30 [PATCH v2] cpu/hotplug: wait for cpuset_hotplug_work to finish on cpu onlining Alexey Klimov
2021-02-12 0:30 ` Alexey Klimov
[not found] ` <20210212003032.2037750-1-aklimov-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2021-02-12 19:41 ` Daniel Jordan
2021-02-12 19:41 ` Daniel Jordan
2021-03-16 3:15 ` Alexey Klimov
[not found] ` <CAFBcO+99Ax5MuOtzNx=NrmnUN=+913Sc-DV83ObOi01A=kkN3w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2021-03-18 19:12 ` Daniel Jordan [this message]
2021-03-18 19:12 ` Daniel Jordan
2021-02-16 18:29 ` Qais Yousef
2021-02-16 18:29 ` Qais Yousef
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