Red Hat Bugzilla – Bug 1300878
[RFE] dnf makecache enabled on readonly-root systems wastes cpu
Last modified: 2016-12-20 13:03:46 EST
Description of problem: It looks like dnf makecache timer that is eanbled by default for some reason cannot understand that it's running on a readonly root system (i.e. nfsroot) and fires anyway, so 10 minutes after system start we end up with dnf makecache process that hogs 100% of cpu. 32441 ? RNs 14:24 /usr/bin/python -OO /usr/bin/dnf -v makecache timer strace shows that it's looping trying to perform: open("/var/cache/dnf/metadata_lock.pid", O_WRONLY|O_CREAT|O_EXCL, 0644) = -1 EEXIST (File exists) open("/var/cache/dnf/metadata_lock.pid", O_RDONLY) = -1 ENOENT (No such file or directory) The file does not exist: # ls -la /var/cache/dnf/metadata_lock.pid ls: cannot access /var/cache/dnf/metadata_lock.pid: No such file or directory The /var/cache/dnf is not one of the default targets to be mounted in tmpfs (and for a good reason). I see that the timer in question already contains a condition against running when started from livecd image: ConditionKernelCommandLine=!rd.live.image Now, if this could be replaced with a check of /etc/sysconfig/readonly-root and not run when READONLY is set to yes - that would be a lot more proper solution. Or at least a check that /var/cache/dnf is actually writeable. Version-Release number of selected component (if applicable): present in all version of dnf starting from FC21 How reproducible: 100% reproducible Steps to Reproduce: If you are not up to the task of doing nfs readonly-root install or the like, you can simulate it by: 1. mount none /var/cache/dnf -t tmpfs 2. mount / /media --bind 3. cp -a /media/var/cache/dnf/* /var/cache/dnf/ 4. umount /media 5. strace dnf makecache Note it's important to do the copying of a real existing dnf cache as otherwise it's smart enough to fail seeing as it cannot create it if the /var/cache/dnf is empty (which it is not on a real readonly nfsroot install) Actual results: dnf enters infinite loop hogging 100% of one cpu. Expected results: should notice that it cannot do anything. Even better if dnf makecache was not run by default in such a case. Additional info: This all got introduced with the mandatory on-by-default dnf makecache timer as part of dnf package, that sparked quite a heated discussion in bug 1187111.
There's one more step in the reproducer, btw, that I forgot to include: 3.5 mount /var/cache/dnf -o remount,ro Otherwise the /var/cache/dnf is not readonly and you won't see the problem.
we can add the readonly checker everytime we load cache directory.
This package has changed ownership in the Fedora Package Database. Reassigning to the new owner of this component.
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