On Fri, Aug 17, 2018 at 10:56 AM David Hildenbrand <da...@redhat.com> 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 <vkuzn...@redhat.com> > >> > >> 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 <vkuzn...@redhat.com> > >> [modify patch description] > >> Signed-off-by: David Hildenbrand <da...@redhat.com> > >> --- > >> 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.