linux-kernel - Re: [PATCH 1/7] work_on_cpu: helper for doing task on a CPU.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20081024132509.GB17708@redhat.com>
Date:	Fri, 24 Oct 2008 15:25:09 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, travis@....com,
	Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>
Subject: Re: [PATCH 1/7] work_on_cpu: helper for doing task on a CPU.

On 10/24, Gautham R Shenoy wrote:
>
> Having a rule that we shouldn't use work_on_cpu() in cpu-hotplug path
> is a good thing. But maintaining it can be difficult.
>
> We've seen that in the past with the cpucontrol mutex.
> We had clear rules that functions which get called in
> cpu-hotplug callback paths, shouldn't take this mutex. But with
> functions that were called in the cpu-hotplug notifier
> path as well as normal paths, it created a whole locking mess,
> and took quite some time to fix.
>
> Similarly, right now, we can have a BUG_ON() which notifies us whenever
> someone ends up calling a function that invokes work_on_cpu() from the
> CPU-Hotplug callpath. But we will fix it only when the BUG_ON() is hit.
>
> On the other hand, if we have a mechanism that's guaranteed to work
> irrespective of the callpaths, why not use that ?

If we add another wq for work_on_cpu(), then we add another hard-to-maintain
rule: get_online_cpus() must not be used by any work which can be queued
on that wq. And, yet another per-cpu thread...

Personally I don't even think we need a BUG_ON() in work_on_cpu(), because
I don't think cpu-hotplug path is so special.

Not that I have a strong opinion though.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/