Most recent kernel where this bug did *NOT* occur: Distribution: Gentoo Hardware Environment: client amd64/server x86 Problem Description: I can't get NFS in v2.6.19+ to mount rw. It says it's mounted rw when I mount -v, it says it's mounted rw when I cat /etc/mtab. When I try to write to the filesystem as root it says it's mounted read-only. I'm really unsure how to debug this. Even worse I'm very unsure how to google this, and have searched the LKML up and down to try to find a solution. I would think this is a configuration problem since it hasn't been reported yet (as far as I can find) but I am definitely able to write to it when I try switching back to 2.6.18.* I attempted to git-bisect (between 2.6.18 and 2.6.19) but haven't had time to finish it. I'm really unsure what information would be useful for this bug report. Steps to reproduce: Boot 2.6.19 (upto the current git of the day) mount nfs directory rw touch /mnt/mydir/touch (fs is mounted ro) Guess I'm not only looking for a solution here, but maybe a bit of help on how I can figure out what this issue could be. Thanks for your time.
See BUG 7612: The VFS does not, and has not ever, allowed you to remount the same filesystem with different mount options. NFS 'allowed' this because if you mounted a different directory, it would treat that as a different filesystem. Unfortunately, that leads to nasty cache consistency problems. As of 2.6.19, NFS will group all directories that belong to the same filesystem on the server into the same superblock and hence treat them as the same filesystem on the client.
Aah! Thanks for the great explanation!