On Thu, Mar 15, 2018 at 10:42:11PM +0200, Amir Goldstein wrote: > On Thu, Mar 15, 2018 at 8:47 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > On Wed, Mar 14, 2018 at 03:15:33PM -0400, Vivek Goyal wrote: > >> On Wed, Mar 07, 2018 at 10:21:30AM +0200, Amir Goldstein wrote: > >> > On Tue, Mar 6, 2018 at 10:54 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > >> > > When a metacopy file is no longer a metacopy and data has been copied up, > >> > > remove REDIRECT xattr. Its not needed anymore. > >> > > > >> > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> > >> > > --- > >> > > fs/overlayfs/copy_up.c | 9 +++++++++ > >> > > 1 file changed, 9 insertions(+) > >> > > > >> > > diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c > >> > > index 0c8d2755bd25..704febd2e2fa 100644 > >> > > --- a/fs/overlayfs/copy_up.c > >> > > +++ b/fs/overlayfs/copy_up.c > >> > > @@ -775,6 +775,15 @@ static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c) > >> > > if (err) > >> > > return err; > >> > > > >> > > + /* > >> > > + * A metacopy files does not need redirect xattr once data has > >> > > + * been copied up. > >> > > + */ > >> > > + err = vfs_removexattr(upperpath.dentry, OVL_XATTR_REDIRECT); > >> > > + if (err && err != -ENODATA && err != -EOPNOTSUPP) > >> > > + return err; > >> > > + > >> > > + err = 0; > >> > > ovl_set_upperdata(d_inode(c->dentry)); > >> > > return err; > >> > > >> > By intuition, I would say that removing redirect should be done after setting > >> > upperdata flag. Not sure if it really matters in real life. > >> > Maybe when racing a lookup of a metacopy hardlink and copy up data of > >> > an upper alias? > >> > >> I think you found a good race situation. > >> > >> > > >> > Also, it would make sense to also ovl_dentry_set_redirect(c->dentry, NULL) > >> > probably use a helper ovl_clear_redirect() for the locking. > >> > > >> > But that highlights a serious problem with current patches - > >> > Access to OVL_I(inode)->redirect is protected with parent mutex in ovl_lookup() > >> > and additionally with dentry->d_lock in ovl_rename() > >> > That is sufficient for directories which can only have a single dentry > >> > alias to an > >> > inode but not at all sufficient for non-directories. > >> > >> This is a good point. So we need to protect OVL_I(inode)->redirect with > >> oi->lock mutex as well (atleast for non-dirs). So ovl_rename() will nest > >> 3 locks (which it already does for index case). > >> > >> parent dir i_mutex. > >> oi->lock > >> dentry->d_lock(). > >> > >> I will try to write a patch for this and see what issues do I face > > > > Hi Amir, > > > > I am trying to understand better how you are taking oi->lock w.r.t > > nlink stuff and I am having a hard time. > > > > - Why do you keep oi->locked for the duration of operation (link, unlink > > etc) using ovl_nlink_start() and ovl_nlink_end(). > > As the comment above ovl_nlink_start() says, union nlink may be changed > by link(), unlink() and copyup. nlink is an overlay inode property, so we need > to protect its updates with a lock on the inode object, which in this level if > oi->lock. Also, in ovl_nlink_end() we cleanup the index on last union nlink drop > and we need to do that also under inode object lock. Sure. What I don't understand is that why do we have to continue to hold the lock for the whole duration. Can we drop the lock and re-acquire it before we cleanup index and change nlink value on ovelray inode? Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
