On Wednesday, April 23, 2014 09:50:32 AM Li Zhong wrote: > On Tue, 2014-04-22 at 12:11 +0200, Rafael J. Wysocki wrote: > > On Tuesday, April 22, 2014 11:34:39 AM Li Zhong wrote: > > > On Mon, 2014-04-21 at 18:46 -0400, Tejun Heo wrote: > > > > Hello, > > > > > > > > On Mon, Apr 21, 2014 at 05:23:50PM +0800, Li Zhong wrote: > > > > > > > > Proper /** function comment would be nice. > > > > > > Ok, will try to write some in next version. > > > > > > > > > > > > +struct kernfs_node *lock_device_hotplug_sysfs(struct device *dev, > > > > > + struct device_attribute > > > > > *attr) > > > > > > > > I can see why you did this but let's please not require the user of > > > > this function to see how the thing is working internally. Let's > > > > return int and keep track of (or look up again) the kernfs_node > > > > internally. > > > > > > Ok, it also makes the prototype of lock and unlock look more consistent > > > and comfortable. > > > > > > > > > > > > { > > > > ... > > > > > + /* > > > > > + * We assume device_hotplug_lock must be acquired before > > > > > removing > > > > > > > > Is this assumption true? If so, can we add lockdep assertions in > > > > places to verify and enforce this? If not, aren't we just feeling > > > > good when the reality is broken? > > > > > > It seems not true ... I think there are devices that don't have the > > > online/offline concept, we just need to add it, remove it, like ethernet > > > cards. > > > > Well, I haven't been following this closely (I was travelling, sorry), but > > there certainly are devices without online/offline. That currently is only > > present for CPUs, memory blocks and ACPI containers (if I remember > > correctly). > > > > > > > > Maybe we could change the comments above, like: > > > /* We assume device_hotplug_lock must be acquired before > > > * removing devices, which have online/offline sysfs knob, > > > * and some locks are needed to serialize the online/offline > > > * callbacks and device removing. ... > > > ? > > > > Lockdep assertions would be better than this in my opinion. > > This is talking about the lock required in the other process, the device > removing process, e.g. that in remove_memory() below. So I guess no > lockdep assertions needed here. Or I misunderstand your point?
I mean if you assume certain lock to be held somewhere, it is better to use lockdep annotations to express that assumption, because that will cause users to *see* the problem when it happens. Thanks! -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/