Miklos Szeredi <miklos@xxxxxxxxxx> writes: > On Wed, 2 Dec 2009, Jeff Layton wrote: >> In the case of a bind mounted file, the path walking code will assume >> that the cached dentry that was bind mounted is valid. This is a problem >> problem for NFSv4 in a way that's similar to LAST_BIND symlinks. >> >> Fix this by revalidating the dentry if FS_FOLLOW_DOT is set and >> __follow_mount returns true. >> >> Note that in the non-open codepath, we cannot return an error to the >> lookup if the revalidation fails. Doing so will leave a bind mount in >> a state such that we can't unmount it. In that case we'll just have to >> settle for d_invalidating it (which should mostly turn out to be a >> d_drop in this case) and returning success. > > The only worry I have is that this adds an extra branch in a very hot > codepath (do_lookup). An error can't be returned, as you note, and > for bind mounted directories d_invalidate() will not succeed: the > directory is busy, it's referenced by the mount. Not true. d_mountpoint is false, so d_invalidate can succeed. > So basically the > only thing this does is working around the NFSv4 issue. No, this should catch other cases where we have a dentry goes stale as well, and lets the distributed filesystem handle it. It is probably worth a benchmark to ease the concerns about the hotpath. I expect the cpu will predict the branch as unlikely and we won't see any difference. Eric -- 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
