On 10.01.20 18:39, Dan Williams wrote: > On Fri, Jan 10, 2020 at 9:36 AM David Hildenbrand <david@xxxxxxxxxx> wrote: >> >> On 10.01.20 18:33, Dan Williams wrote: >>> On Fri, Jan 10, 2020 at 9:29 AM David Hildenbrand <david@xxxxxxxxxx> wrote: >>> [..] >>>>> So then the comment is actively misleading for that case. I would >>>>> expect an explicit _unlocked path for that case with a comment about >>>>> why it's special. Is there already a comment to that effect somewhere? >>>>> >>>> >>>> __add_memory() - the locked variant - is called from the same ACPI location >>>> either locked or unlocked. I added a comment back then after a longe >>>> discussion with Michal: >>>> >>>> drivers/acpi/scan.c: >>>> /* >>>> * Although we call __add_memory() that is documented to require the >>>> * device_hotplug_lock, it is not necessary here because this is an >>>> * early code when userspace or any other code path cannot trigger >>>> * hotplug/hotunplug operations. >>>> */ >>>> >>>> >>>> It really is a special case, though. >>> >>> That's a large comment block when we could have just taken the lock. >>> There's probably many other code paths in the kernel where some locks >>> are not necessary before userspace is up, but the code takes the lock >>> anyway to minimize the code maintenance burden. Is there really a >>> compelling reason to be clever here? >> >> It was a lengthy discussion back then and I was sharing your opinion. I >> even had a patch ready to enforce that we are holding the lock (that's >> how I identified that specific case in the first place). > > Ok, apologies I missed that opportunity to back you up. Michal, is > this still worth it? > For your reference (roughly 5 months ago, so not that old) https://lkml.kernel.org/r/20190724143017.12841-1-david@xxxxxxxxxx -- Thanks, David / dhildenb
