On Mon, Oct 31, 2011 at 5:16 AM, Tejun Heo <tj@xxxxxxxxxx> wrote: > (cc'ing Rafael and linux-pm) > > On Sat, Oct 29, 2011 at 11:48:21PM -0500, David Fries wrote: >> I saw the write up on this on lwn.net, pretty creative by the way, and >> it got me thinking about a different checkpoint/restart problem I've >> been running into. Specifically in hibernating to disk. In the >> hibernate case active TCP connections hang after resuming, while an >> idle TCP connection will continue after the system is back up. My >> observation is the kernel checkpoints itself to memory, enables >> devices, writes out that checkpoint image to storage, then powers off. >> The problem is if TCP packets are received while writing to storage, >> the kernel will continue to queue and ack those TCP packets, but the >> running kernel and it's network state is shortly lost. When the >> computer resumes, those TCP byte sequences hang the TCP connection for >> an extended period of time while the resumed computer refuses to >> acknowledge the data that was received after checkpointing and the now >> running kernel knew nothing about, and the other computer tries in >> vain to resend any data that hadn't yet been acknowledged, which is >> always after the data that was lost, until one of them eventually >> gives up. >> >> I've been wondering if it was safe or possible to leave any network >> interfaces down after the checkpoint, or what the right solution would >> be. I didn't think marking every TCP connection with a ZOMBIE_KERNEL >> bit just after the kernel checkpoint (for the kernel is walking dead >> and won't remember anything that happens), and then prevent any TCP >> acks from being sent for those connections would be the right >> solution. I've taken to unplugging the physical lan cable, >> hibernating to disk, and plugging it back in after the system is down, >> to avoid the problem. Any ideas? > > Hmmm... sounds like taking down network interfaces before starting > hibernation sequence should be enough, which shouldn't be too > difficult to implement from userland. Rafael, what do you think? > > Thanks. Um... it seems that the "thaw" callbacks of network interfaces or TCP should do something on this. Probably, the "thaw" callbacks should make sure that the TCP connections are closed? Cheers, MyungJoo > > -- > tejun > _______________________________________________ > linux-pm mailing list > linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > https://lists.linuxfoundation.org/mailman/listinfo/linux-pm > -- MyungJoo Ham, Ph.D. Mobile Software Platform Lab, DMC Business, Samsung Electronics _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
