tree 16696a688d5b6386c6183cc6137807af38e1d9d1
parent cf31e70d6cf93f19fe9bf1144966ef40991ac723
author Al Viro <viro@zeniv.linux.org.uk> 1325642489 -0500
committer Al Viro <viro@zeniv.linux.org.uk> 1325649190 -0500

vfs: fix the rest of sget() races

unfortunately, just checking MS_BORN after having grabbed ->s_umount in
sget() is not enough; places that pick superblock from a list and
grab s_umount shared need the same check in addition to checking for
->s_root; otherwise three-way race between failing mount, sget() and
such list-walker can leave us with list-walker coming *second*, when
temporary active ref grabbed by sget() (to be dropped when sget()
notices that original mount has failed by checking MS_BORN) has
lead to deactivate_locked_super() from failing ->mount() *not* doing
->kill_sb() and just releasing ->s_umount.  Once sget() gets through
and notices that MS_BORN had never been set it will drop the active
ref and fs will be shut down and kicked out of all lists, but it's
too late for something like sync_supers().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>