emerging =sys-fs/lvm2-2.00.25 with the 'readline' USE flag enabled causes critical LVM2 applications (like vgscan) to be linked against ncurses and, when ncurses has been emerged with the 'gpm' USE flag, against gpm. the problem is that libgpm.so.1 resides in /usr/lib and not in /lib like the others.
now imagine what happens when you have your /usr on an LVM2 volume :>
right, your system doesn't boot because vgscan aborts.
here is a list of the corresponding entries from a "ldd /sbin/vgscan":
libncursesw.so.5 => /lib/libncursesw.so.5 (0x0000002a95695000)
libgpm.so.1 => /usr/lib/libgpm.so.1 (0x0000002a95a04000)
they disappear when using USE="-readline" when emerging lvm2.
suggestions: either move libgpm to /lib or never ever use readline when merging lvm2.
This is the same as #80403
*** This bug has been marked as a duplicate of 80403 ***