[LU-7086] RHEL made /sbin a symlink to /usr/sbin/

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.8.0
• Severity: 3
• Assignee: Emoly Liu
• Reporter: Oleg Drokin

Description

We have a code in test-framework.sh that tries to avoid double-mounting /sbin/mount.lustre when running from a built tree:

       local mount_lustre=$LUSTRE/utils/mount.lustre
        if [ -f $mount_lustre ]; then
                local sbin_mount=/sbin/mount.lustre
                if grep -qw "$sbin_mount" /proc/mounts; then
                        cmp -s $mount_lustre $sbin_mount || umount $sbin_mount
                fi

In rhel7 and other new distros with the /sbin -> /usr/sbin symlink that never matches, /proc/mounts output is like this:

192.168.10.1:/exports/centos7-nfsroot/home/green/git/lustre-release/lustre/utils/mount.lustre /usr/sbin/mount.lustre nfs4 rw,relatime,vers=4.0,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.10.232,local_lock=none,addr=192.168.10.1 0 0

This is sounds mostly harmless, after all whats acouple of more bind mounts, right? Except for an unknown reason (I am still looking), rhel7 kernel is doubling size of mnt_cache slab on every such bind mount, so 7 iterations in the cache takes 120 megabytes, next iteration brings it to 240 and so on. It does add up quickly and some other slabs also grow (though not as drastically), so we quickly run out of memory (I tried and rhel6 kernel does not have this problem).