Re: [PATCH] mm, add_memory_resource: hold device_hotplug lock over mem_hotplug_{begin, done}

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] mm, add_memory_resource: hold device_hotplug lock over mem_hotplug_{begin, done}
Date	2017-03-09 07:40 +0100
Message-ID	<tiZTX-1bv-9@gated-at.bofh.it> (permalink)
References	(3 earlier) <tgcb1-3ud-59@gated-at.bofh.it> <tgePx-5b2-39@gated-at.bofh.it> <tglnX-1pB-5@gated-at.bofh.it> <tglnX-1pB-3@gated-at.bofh.it> <thWbL-5q5-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Mar 6, 2017 at 12:22 AM, Heiko Carstens
<heiko.carstens@de.ibm.com> wrote:
> Hello Dan,
>
>> > If you look at commit 5e33bc4165f3 ("driver core / ACPI: Avoid device hot
>> > remove locking issues") then lock_device_hotplug_sysfs() was introduced to
>> > avoid a different subtle deadlock, but it also sleeps uninterruptible, but
>> > not for more than 5ms ;)
>> >
>> > However I'm not sure if the device hotplug lock should also be used to fix
>> > an unrelated bug that was introduced with the get_online_mems() /
>> > put_online_mems() interface. Should it?
>>
>> No, I don't think it should.
>>
>> I like your proposed direction of creating a new lock internal to
>> mem_hotplug_begin() to protect active_writer, and stop relying on
>> lock_device_hotplug to serve this purpose.
>>
>> > If so, we need to sprinkle around a couple of lock_device_hotplug() calls
>> > near mem_hotplug_begin() calls, like Sebastian already started, and give it
>> > additional semantics (protecting mem_hotplug.active_writer), and hope it
>> > doesn't lead to deadlocks anywhere.
>>
>> I'll put your proposed patch through some testing.
>
> On s390 it _seems_ to work. Did it pass your testing too?
> If so I would send a patch with proper patch description for inclusion.

Looks ok here. No lockdep warnings running it through it paces with
the persistent memory use case.

Thread

Re: [PATCH] mm, add_memory_resource: hold device_hotplug lock over  mem_hotplug_{begin, done} Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-03-01 14:10 +0100
  Re: [PATCH] mm, add_memory_resource: hold device_hotplug lock over  mem_hotplug_{begin, done} Dan Williams <dan.j.williams@intel.com> - 2017-03-01 17:00 +0100
    Re: [PATCH] mm, add_memory_resource: hold device_hotplug lock over  mem_hotplug_{begin, done} Dan Williams <dan.j.williams@intel.com> - 2017-03-02 00:00 +0100
      Re: [PATCH] mm, add_memory_resource: hold device_hotplug lock over  mem_hotplug_{begin, done} Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-03-06 09:30 +0100
        Re: [PATCH] mm, add_memory_resource: hold device_hotplug lock over  mem_hotplug_{begin, done} Dan Williams <dan.j.williams@intel.com> - 2017-03-09 07:40 +0100
    Re: [PATCH] mm, add_memory_resource: hold device_hotplug lock over  mem_hotplug_{begin, done} Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-03-02 01:30 +0100

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