Messages in this thread | | | Subject | Re: About the try to remove cross-release feature entirely by Ingo | From | Byungchul Park <> | Date | Wed, 3 Jan 2018 11:28:44 +0900 |
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On 1/1/2018 7:18 PM, Matthew Wilcox wrote: > On Sat, Dec 30, 2017 at 06:00:57PM -0500, Theodore Ts'o wrote: >> On Sat, Dec 30, 2017 at 05:40:28PM -0500, Theodore Ts'o wrote: >>> On Sat, Dec 30, 2017 at 12:44:17PM -0800, Matthew Wilcox wrote: >>>> >>>> I'm not sure I agree with this part. What if we add a new TCP lock class >>>> for connections which are used for filesystems/network block devices/...? >>>> Yes, it'll be up to each user to set the lockdep classification correctly, >>>> but that's a relatively small number of places to add annotations, >>>> and I don't see why it wouldn't work. >>> >>> I was exagerrating a bit for effect, I admit. (but only a bit). > > I feel like there's been rather too much of that recently. Can we stick > to facts as far as possible, please? > >>> It can probably be for all TCP connections that are used by kernel >>> code (as opposed to userspace-only TCP connections). But it would >>> probably have to be each and every device-mapper instance, each and >>> every block device, each and every mounted file system, each and every >>> bdi object, etc. >> >> Clarification: all TCP connections that are used by kernel code would >> need to be in their own separate lock class. All TCP connections used >> only by userspace could be in their own shared lock class. You can't >> use a one lock class for all kernel-used TCP connections, because of >> the Network Block Device mounted on a local file system which is then >> exported via NFS and squirted out yet another TCP connection problem. > > So the false positive you're concerned about is write-comes-in-over-NFS > (with socket lock held), NFS sends a write request to local filesystem, > local filesystem sends write to block device, block device sends a > packet to a socket which takes that socket lock. > > I don't think we need to be as drastic as giving each socket its own lock > class to solve this. All NFS sockets can be in lock class A; all NBD > sockets can be in lock class B; all user sockets can be in lock class > C; etc. > >> Also, what to do with TCP connections which are created in userspace >> (with some authentication exchanges happening in userspace), and then >> passed into kernel space for use in kernel space, is an interesting >> question. > > Yes! I'd love to have a lockdep expert weigh in here. I believe it's > legitimate to change a lock's class after it's been used, essentially > destroying it and reinitialising it. If not, it should be because it's > a reasonable design for an object to need different lock classes for > different phases of its existance.
I also think it should be done ultimately. And I think it's very much hard since it requires to change the dependency graph of lockdep but anyway possible. It's up to lockdep maintainer's will though..
-- Thanks, Byungchul
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