From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f198.google.com (mail-pf1-f198.google.com [209.85.210.198]) by kanga.kvack.org (Postfix) with ESMTP id EBD546B07A3 for ; Fri, 17 Aug 2018 06:06:08 -0400 (EDT) Received: by mail-pf1-f198.google.com with SMTP id q21-v6so3431944pff.21 for ; Fri, 17 Aug 2018 03:06:08 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id j193-v6si1619695pge.617.2018.08.17.03.06.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 Aug 2018 03:06:07 -0700 (PDT) Date: Fri, 17 Aug 2018 12:06:04 +0200 From: Greg Kroah-Hartman Subject: Re: [PATCH RFC 1/2] drivers/base: export lock_device_hotplug/unlock_device_hotplug Message-ID: <20180817100604.GA18164@kroah.com> References: <20180817075901.4608-1-david@redhat.com> <20180817075901.4608-2-david@redhat.com> <20180817084146.GB14725@kroah.com> <5a5d73e9-e4aa-ffed-a2e3-8aef64e61923@redhat.com> <42df9062-f647-3ad6-5a07-be2b99531119@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <42df9062-f647-3ad6-5a07-be2b99531119@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand Cc: "Rafael J. Wysocki" , Michal Hocko , Benjamin Herrenschmidt , Heiko Carstens , Linux Memory Management List , Paul Mackerras , linux-s390@vger.kernel.org, sthemmin@microsoft.com, Pavel Tatashin , ACPI Devel Maling List , David Rientjes , xen-devel@lists.xenproject.org, Len Brown , haiyangz@microsoft.com, Dan Williams , Andrew Morton , Vlastimil Babka , osalvador@suse.de, "Rafael J. Wysocki" , Linux Kernel Mailing List , Martin Schwidefsky , devel@linuxdriverproject.org, Vitaly Kuznetsov , linuxppc-dev On Fri, Aug 17, 2018 at 11:41:24AM +0200, David Hildenbrand wrote: > On 17.08.2018 11:03, Rafael J. Wysocki wrote: > > On Fri, Aug 17, 2018 at 10:56 AM David Hildenbrand wrote: > >> > >> On 17.08.2018 10:41, Greg Kroah-Hartman wrote: > >>> On Fri, Aug 17, 2018 at 09:59:00AM +0200, David Hildenbrand wrote: > >>>> From: Vitaly Kuznetsov > >>>> > >>>> Well require to call add_memory()/add_memory_resource() with > >>>> device_hotplug_lock held, to avoid a lock inversion. Allow external modules > >>>> (e.g. hv_balloon) that make use of add_memory()/add_memory_resource() to > >>>> lock device hotplug. > >>>> > >>>> Signed-off-by: Vitaly Kuznetsov > >>>> [modify patch description] > >>>> Signed-off-by: David Hildenbrand > >>>> --- > >>>> drivers/base/core.c | 2 ++ > >>>> 1 file changed, 2 insertions(+) > >>>> > >>>> diff --git a/drivers/base/core.c b/drivers/base/core.c > >>>> index 04bbcd779e11..9010b9e942b5 100644 > >>>> --- a/drivers/base/core.c > >>>> +++ b/drivers/base/core.c > >>>> @@ -700,11 +700,13 @@ void lock_device_hotplug(void) > >>>> { > >>>> mutex_lock(&device_hotplug_lock); > >>>> } > >>>> +EXPORT_SYMBOL_GPL(lock_device_hotplug); > >>>> > >>>> void unlock_device_hotplug(void) > >>>> { > >>>> mutex_unlock(&device_hotplug_lock); > >>>> } > >>>> +EXPORT_SYMBOL_GPL(unlock_device_hotplug); > >>> > >>> If these are going to be "global" symbols, let's properly name them. > >>> device_hotplug_lock/unlock would be better. But I am _really_ nervous > >>> about letting stuff outside of the driver core mess with this, as people > >>> better know what they are doing. > >> > >> The only "problem" is that we have kernel modules (for paravirtualized > >> devices) that call add_memory(). This is Hyper-V right now, but we might > >> have other ones in the future. Without them we would not have to export > >> it. We might also get kernel modules that want to call remove_memory() - > >> which will require the device_hotplug_lock as of now. > >> > >> What we could do is > >> > >> a) add_memory() -> _add_memory() and don't export it > >> b) add_memory() takes the device_hotplug_lock and calls _add_memory() . > >> We export that one. > >> c) Use add_memory() in external modules only > >> > >> Similar wrapper would be needed e.g. for remove_memory() later on. > > > > That would be safer IMO, as it would prevent developers from using > > add_memory() without the lock, say. > > > > If the lock is always going to be required for add_memory(), make it > > hard (or event impossible) to use the latter without it. > > > > If there are no objections, I'll go into that direction. But I'll wait > for more comments regarding the general concept first. It is the middle of the merge window, and maintainers are really busy right now. I doubt you will get many review comments just yet...