[I think this is fsdevel material, please let me know if I should be posting elsewhere] I have been investigating some odd failures in Jenkins CI set up, where expect reports 'Out of ptys'. The cause seems to be that when schroot sessions are terminated, the unmount of /path/to/chroot/dev/pts affects the wrong mount point. I can reproduce the problem like this: (using Xubuntu15.10 LiveCD inside qemu, same thing with Fedora and mainline 4.3) root@xubuntu:~# uname -a Linux xubuntu 4.2.0-16-generic #19-Ubuntu SMP Thu Oct 8 15:35:06 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux root@xubuntu:~# mkdir tmp1 tmp2 root@xubuntu:~# mount -o bind /dev tmp1 root@xubuntu:~# mount -o bind /dev/pts tmp1/pts root@xubuntu:~# mount -o bind /dev tmp2 root@xubuntu:~# mount -o bind /dev/pts tmp2/pts root@xubuntu:~# ls tmp1/pts 0 2 3 4 5 6 7 ptmx root@xubuntu:~# ls tmp2/pts 0 2 3 4 5 6 7 ptmx root@xubuntu:~# umount tmp1/pts root@xubuntu:~# ls tmp1/pts # <--- expect this to be empty 0 2 3 4 5 6 7 ptmx root@xubuntu:~# ls tmp2/pts # <--- expect some pty device nodes root@xubuntu:~# It appears that "umount tmp1/pts" actually unmounted tmp2/pts. Also interesting to note is the strange contents of /proc/mounts after the 4 mount commands root@xubuntu:~# mount -o bind /dev tmp1 root@xubuntu:~# mount -o bind /dev/pts tmp1/pts root@xubuntu:~# mount -o bind /dev tmp2 root@xubuntu:~# mount -o bind /dev/pts tmp2/pts root@xubuntu:~# grep pts /proc/mounts devpts /dev/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 devpts /home/xubuntu/tmp1/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 devpts /dev/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 devpts /home/xubuntu/tmp2/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 devpts /dev/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 devpts /home/xubuntu/tmp1/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 /dev/pts appears to be mounted 3 times, and tmp1/pts is mounted twice. Using Ubuntu 14.04, I get this result, which is what I expect to see: root@sale:/root# uname -a Linux sale 3.13.0-71-generic #114-Ubuntu SMP Tue Dec 1 02:34:22 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux root@sale:/root# mount -o bind /dev tmp1 root@sale:/root# mount -o bind /dev/pts tmp1/pts root@sale:/root# mount -o bind /dev tmp2 root@sale:/root# mount -o bind /dev/pts tmp2/pts root@sale:/root# grep pts /proc/mounts devpts /dev/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 devpts /root/tmp1/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 devpts /root/tmp2/pts devpts rw,nosuid,noexec,relatime,mode=600,ptmxmode=000 0 0 It would be useful to know whether this is invalid use of bind mounts, or if it's really a bug. Thanks Charles -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
