I suggest reproducing the problem and issuing sysrq+w and then post the entire resulting output for a developer to evaluate. I find it's best to have the sysrq setup in a shell before hand so all you have to do is hit return, and of course you can test the before the problem happens. It dumps to dmesg and can sometimes overflow the default size buffer, so either increase the buffer, or get it from 'journalctl -k' redirected to a file. The entire kernel message might be helpful, but I also note the kernel isn't tainted so what you're getting is mostly info noise about the hang. I see this is btrfs-receive workload, so I wouldn't guess it's suvolume lock contention unless the contention is happening with a single shared parent subvolume into which all the receive subvolumes are going (e.g. subvol id 5). I'm not sure how to alleviate it. Chris Murphy Chris Murphy
