On Fri, Nov 08, 2013 at 12:51:52PM -0800, Eric W. Biederman wrote: > The return value of d_mountpoint can be obsolete as soon as it returns > as well, so I don't see this as being significantly different. Not if the ->i_mutex of that sucker is held. And it *is* held in vfs_unlink/vfs_rmdir/vfs_rename. Note that we only care about a mountpoint being falsely assumed to be a non-mountpoint - in the other direction we can just shrug and say that we'd won the race and got EBUSY for that. > In 3.12 vfs_rmdir checks d_mountpoint with the > dentry->d_inode->i_mutex and > dentry->d_parent->d_inode->i_mutex held. > > In 3.12 vfs_unlink checks d_mountpoint with the > dentry->d_inode->i_mutex and > dentry->d_parent->d_inode->i_mutex hel.d > > In 3.12 vfs_rename_dir and vfs_rename_other checks d_mountpint with the > target->i_mutex, new_dir->i_mutex, and old_dir->i_mutex held. > > > Therefore the guarantees in 3.12 are: > - unlink versus mount races are prevented by the > dentry->d_inode->i_mutex of the dentry being removed. > - unlink versus umount races are uninteresting. > - mount versus rename races in testing of d_mountpoint are ignored. Read what you've written a few lines above. The part about target->i_mutex being held. > So comparing this to how I have implemented covered the test is at a > slightly different location in the call path so there may be a slightly > larger race in rename. You've got a race in unlink. You've got a race in rename. You've got a race in rmdir. And none of those had that race in 3.12 (including rename()). BTW, could you describe the races with umount in a bit more details? Races with mount are simple - rmdir() sees that victim isn't a mountpoint and proceeds, mount() sees that victim is still alive and proceeds, despite the fact that victim is irretrievably on the way to removal. And that's what ->i_mutex on victim prevents, making "check for d_mountpoint / remove / call dont_mount()" atomic wrt mount(). What is the problem you are seeing with umount()? rmdir() getting EBUSY because it hasn't noticed umount() happening in parallel with it? Legitimate behaviour, as far I can see... Or is it about something different? -- 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
