On Fri, Oct 22, 2010 at 06:14:01PM +0200, Miklos Szeredi wrote: > @@ -1782,6 +1844,14 @@ int do_add_mount(struct vfsmount *newmnt > > mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL); Obviously not enough - you've just added a new flag that needs to be trimmed from mnt_flags. > + /* Locking is necessary to prevent racing with remount r/o */ > + down_read(&newmnt->mnt_sb->s_umount); > + if (newmnt->mnt_sb->s_flags & MS_RDONLY) > + mnt_flags |= MNT_READONLY; > + > + newmnt->mnt_flags = mnt_flags; > + up_read(&newmnt->mnt_sb->s_umount); FWIW, I really don't like the way you are doing that; what we really need there is a per-sb analog of mnt_want_write()/mnt_drop_write(). With mnt_want_write() bumping per-sb write count, which would solve all these problems quite nicely. NOTE: vfsmount being ro and sb being ro are *independent* things; either is enough to deny writes. Having remount ro + remount rw lose the state of other vfsmounts is a Bad Thing(tm). Another thing: "If clone_mnt() happens while mnt_make_readonly() is running, the cloned mount might have MNT_WRITE_HOLD flag set, which results in mnt_want_write() spinning forever on this mount." actually means "neither clone_mnt() nor remounts should ever be done without namespace_sem held exclusive; if that ever happens, we have a serious bug that can lead to any number of bad things happening". Do you actually see such places? If so, that's what needs fixing. -- 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
