On Tue, 2013-07-02 at 11:42 +1000, NeilBrown wrote: > On Mon, 1 Jul 2013 09:20:30 -0400 Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > Christopher reported a regression where he was unable to unmount a NFS > > filesystem where the root had gone stale. The problem is that > > d_revalidate handles the root of the filesystem differently from other > > dentries, but d_weak_revalidate does not. We could simply fix this by > > making d_weak_revalidate return success on IS_ROOT dentries, but there > > are cases where we do want to revalidate the root of the fs. > > > > A umount is really a special case. We generally aren't interested in > > anything but the dentry and vfsmount that's attached at that point. If > > the inode turns out to be stale we just don't care since the intent is > > to stop using it anyway. > > > > Try to handle this situation better by treating umount as a special > > case in the lookup code. Have it resolve the parent using normal > > means, and then do a lookup of the final dentry without revalidating > > it. In most cases, the final lookup will come out of the dcache, but > > the case where there's a trailing symlink or !LAST_NORM entry on the > > end complicates things a bit. > > > > Reported-by: Christopher T Vogan <cvogan@xxxxxxxxxx> > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > Thanks for this Jeff. It certainly looks credible to me. > > There is a lot of code copied from the "user_path_at" path which is a shame, > but probably better that putting in lots of "is this an unmount" tests which > would slow done the common case. > > On balance, I like it. > > Thanks, > NeilBrown > (cc'ing Christopher as I mistakenly left him off the original mail. I'll make sure to cc him on any respins...) Thanks for looking. Yeah it is a lot of code to handle one case. So, while this does seem to work, I'm still not 100% sold on this approach... I had assumed that we would sometimes want to revalidate IS_ROOT dentries in other codepaths. Now that I think about it though, I'm having a hard time coming up with any situations where that's necessary. We'll never want to invalidate such a dentry, so does that ever make sense? If it doesn't, we could just replace this patch with a test for IS_ROOT(dentry) in nfs_weak_revalidate, and call it a day. I tested a patch like that earlier and it also worked around the problem. Also, it bothers me a little that this patch stops revalidating anything once it hits the last component, even if it's a symlink and we know we'll have to chase it down. It may make sense to check for d_mountpoint in some cases and revalidate the dentry if it's true. Thoughts? -- Jeffrey Layton <jlayton@xxxxxxxxxx> -- 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
