Date: Wed, 24 Feb 2021 15:37:12 -0800 From: Ravi Pokala <rpokala@freebsd.org> To: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: `sysctl vm.pmap.kernel_maps' spins on 12.2-RELEASE-p3 w/ nvdimm.ko Message-ID: <2C7B4C6A-0432-44A6-B512-D7114F2B092B@freebsd.org>
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Hi folks, A colleague and I both independently observed `sysctl -a' appear to hang on nodes running FreeBSD 12.2-RELEASE-p3; it didn't emit any output, and ^C didn't kill it. We could still establish a new terminal session to the node, via SSH or serial console, and we were able to see that it was actually spinning, not hung, and was consuming an entire CPU. We eventually determined that it was specifically `sysctl vm.pmap.kernel_maps' which was spinning, and subsequently that it only spinned if nvdimm.ko was loaded. It was not necessary to access the device node associated with the NVDIMM; merely having the module loaded was sufficient. I know nvdimm(4) isn't terribly widely used, but hopefully someone who uses it can at least confirm my findings on this. Help in debugging would be even more appreciated. Thanks, Ravi (rpokala@)
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