Comment # 9 on bug 1231836 from Wenruo Qu

BTW, I also explored another solution, to allow mismatch in sb->s_flags and
fc->sb_flags, then reconfigure.
This methods avoid the brute force retry loop, and use proper rwsem to prevent
race in theory.

But it just doesn't work.

If the fs is initially mounted RO, a new RW open on the same device will return
-EINVAL, thus rejecting the mount way earlier before we can get a proper super
block to continue.

That's why we're risking the race by retry without a proper sb lock to hold.