On Wed, Oct 16, 2013 at 01:04:07AM -0700, Christoph Hellwig wrote:
> On Tue, Oct 15, 2013 at 04:39:33PM -0400, J. Bruce Fields wrote:
> > From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
> >
> > We shouldn't really have to re-lookup the parents on each pass through.
> > This should make behavior linear instead of quadratic as a function of
> > directory depth.
>
> This looks valid after going through the nasty cases like a
> cross-directory rename. But I'd really prefer the changelog to be way
> more detailed.
>
> Also a few untested fixups below:
> - document that reconnect_one can only be called for directories
> - make sure we always properly drop the parent dentry on
> reconnect_one failure
> - warn then the tmp dentry is not the same as the one we started
> with. Given that we deal with directories this should not
> happen
> - add/update a few comments.
> - tidy up the reconnect_path loop so the reconnect case shares
> more logic with the dget_parent case
>
>
> Index: linux/fs/exportfs/expfs.c
> ===================================================================
> --- linux.orig/fs/exportfs/expfs.c 2013-10-16 09:58:44.544119517 +0200
> +++ linux/fs/exportfs/expfs.c 2013-10-16 10:04:19.176127470 +0200
> @@ -104,38 +104,30 @@ static void clear_disconnected(struct de
> }
>
> /*
> - * Return the parent directory on success.
> + * Reconnect a directory dentry with its parent.
> *
> - * If it races with a rename or unlink, assume the other operation
> - * connected it, but return NULL to indicate the caller should check
> - * this just to make sure the filesystem isn't nuts.
> + * Return the parent directory when successfully reconnecting, NULL if it
> + * raced with another VFS operation, in which case it got connected or
> + * the whole file handle will become stale.
> *
> * Otherwise return an error.
> */
> -static struct dentry *reconnect_one(struct vfsmount *mnt, struct dentry *dentry, char *nbuf)
> +static struct dentry *reconnect_one(struct vfsmount *mnt,
> + struct dentry *dentry, char *nbuf)
> {
> struct dentry *parent;
> struct dentry *tmp;
> int err;
> - /*
> - * Getting the parent can't be supported generically, the
> - * locking is too icky.
> - *
> - * If it can't be done, we just return EACCES. If you were
> - * depending on the dcache finding the parent for you, you lose
> - * if there's a reboot or inodes get flushed.
> - */
> - parent = ERR_PTR(-EACCES);
>
> + parent = ERR_PTR(-EACCES);
> mutex_lock(&dentry->d_inode->i_mutex);
> if (mnt->mnt_sb->s_export_op->get_parent)
> parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
> mutex_unlock(&dentry->d_inode->i_mutex);
>
> if (IS_ERR(parent)) {
> - err = PTR_ERR(parent);
> dprintk("%s: get_parent of %ld failed, err %d\n",
> - __func__, dentry->d_inode->i_ino, err);
> + __func__, dentry->d_inode->i_ino, PTR_ERR(parent));
> return parent;
> }
>
> @@ -143,26 +135,45 @@ static struct dentry *reconnect_one(stru
> dentry->d_inode->i_ino, parent->d_inode->i_ino);
> err = exportfs_get_name(mnt, parent, nbuf, dentry);
> if (err) {
> + /*
> + * Someone must have renamed our entry into another parent,
> + * in which case it has been reconnected by the rename.
> + *
> + * Or someone removed it entirely, in which case the file
> + * handle has become stale.
> + */
> if (err == -ENOENT)
> - return NULL;
> - dput(parent);
> - return ERR_PTR(err);
> + goto out_reconnected;
> + goto out_err;
> }
> dprintk("%s: found name: %s\n", __func__, nbuf);
> mutex_lock(&parent->d_inode->i_mutex);
> tmp = lookup_one_len(nbuf, parent, strlen(nbuf));
> mutex_unlock(&parent->d_inode->i_mutex);
> if (IS_ERR(tmp)) {
> - err = PTR_ERR(tmp);
> - dprintk("%s: lookup failed: %d\n",
> - __func__, err);
> - return NULL;
> + dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
> + goto out_reconnected;
> + }
> + if (WARN_ON(tmp != dentry)) {
> + dprintk("%s: got different dentry while reconnecting.\n",
> + __func__);
> + dput(tmp);
> + err = -ESTALE;
> + goto out_err;
Wait, no, this isn't right. This isn't a multiple-directory-alias case.
It's just another "out_reconnected" case. Somebody renamed or removed
between get_name and lookup_one_len and lookup_one_len() and now
whatever lookup_one_len() finds could be something totally different.
--b.
> }
> - /* Note tmp != dentry is possible at this point, but that's OK */
> dput(tmp);
> - if (IS_ROOT(dentry))
> - return ERR_PTR(-ESTALE);
> + if (IS_ROOT(dentry)) {
> + err = -ESTALE;
> + goto out_err;
> + }
> return parent;
> +
> +out_err:
> + dput(parent);
> + return ERR_PTR(err);
> +out_reconnected:
> + dput(parent);
> + return NULL;
> }
>
> /*
> @@ -178,21 +189,18 @@ reconnect_path(struct vfsmount *mnt, str
> dentry = dget(target_dir);
>
> while (dentry->d_flags & DCACHE_DISCONNECTED) {
> - if (dentry == mnt->mnt_sb->s_root) {
> - WARN_ON_ONCE(1);
> - break;
> - }
> - if (!IS_ROOT(dentry)) {
> + BUG_ON(dentry == mnt->mnt_sb->s_root);
> +
> + if (IS_ROOT(dentry)) {
> + /*
> + * We have hit the top of a disconnected path, try to
> + * find parent and connect.
> + */
> + parent = reconnect_one(mnt, dentry, nbuf);
> + } else {
> parent = dget_parent(dentry);
> - dput(dentry);
> - dentry = parent;
> - continue;
> }
> - /*
> - * We have hit the top of a disconnected path, try to
> - * find parent and connect.
> - */
> - parent = reconnect_one(mnt, dentry, nbuf);
> +
> dput(dentry);
> if (!parent)
> break;
> @@ -200,6 +208,7 @@ reconnect_path(struct vfsmount *mnt, str
> return PTR_ERR(parent);
> dentry = parent;
> }
> +
> /*
> * Should be unnecessary, but let's be careful:
> */
--
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