On Mon, Jul 18, 2011 at 02:42:51PM -0700, Linus Torvalds wrote: > On Mon, Jul 18, 2011 at 2:19 PM, Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > > > __d_lookup_rcu() is being careful about *inode, yes. > > > > But I'd forgotten it was even setting it: doesn't that setting get > > overridden later by the more careless *inode = path->d_entry->d_inode > > at the head of __follow_mount_rcu()'s loop? > > > > Perhaps that line just needs to be moved to the tail of the loop? > > Ahh. Bingo. Yes, I think you found it. > > I don't think it should touch that *inode value in > __follow_mount_rcu() unless we actually followed a mount, exactly > because it will overwrite the thing that we were so careful about in > __d_lookup_rcu(). > > So how about this patch that replaces the earlier mount-point sequence > number one. The only difference is (as you mention) to just do the > *inode update at the end of the loop, so that we don't overwrite the > valid inode data with a non-checked one when we don't do anything. > > Untested. But this should make my propised change to fs/dcache.c be > irrelevant, because whether we clear d_inode or not, the existing > sequence number checks will catch it. Agreed? You know what... I doubt that you want to mess with ->d_seq checks here. It's definitely not Hugh's bug (unless he has bindings somewhere odd) and both ->mnt_mountpoint and ->mnt_root are pinned (and we are holding vfsmount_lock anyway). *inode assignment too early is a real bug, indeed, and we want to assign nd->seq if we cross mountpoint as both versions do, but check just before that is, in the best case, BUG_ON() fodder. We'd just found a vfsmount with ->mnt_mountpoint equal to path->dentry; it *can't* be stale, or we have a really nasty problem anyway. -- 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
