linux-kernel - [PATCH 4.14 11/71] Btrfs: fix stale entries in readdir

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Date:   Mon, 29 Jan 2018 13:56:39 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Josef Bacik <jbacik@...com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 4.14 11/71] Btrfs: fix stale entries in readdir

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Josef Bacik <jbacik@...com>

commit e4fd493c0541d36953f7b9d3bfced67a1321792f upstream.

In fixing the readdir+pagefault deadlock I accidentally introduced a
stale entry regression in readdir.  If we get close to full for the
temporary buffer, and then skip a few delayed deletions, and then try to
add another entry that won't fit, we will emit the entries we found and
retry.  Unfortunately we delete entries from our del_list as we find
them, assuming we won't need them.  However our pos will be with
whatever our last entry was, which could be before the delayed deletions
we skipped, so the next search will add the deleted entries back into
our readdir buffer.  So instead don't delete entries we find in our
del_list so we can make sure we always find our delayed deletions.  This
is a slight perf hit for readdir with lots of pending deletions, but
hopefully this isn't a common occurrence.  If it is we can revist this
and optimize it.

Fixes: 23b5ec74943f ("btrfs: fix readdir deadlock with pagefault")
Signed-off-by: Josef Bacik <jbacik@...com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/delayed-inode.c |   26 ++++++++------------------
 1 file changed, 8 insertions(+), 18 deletions(-)

--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1677,28 +1677,18 @@ void btrfs_readdir_put_delayed_items(str
 int btrfs_should_delete_dir_index(struct list_head *del_list,
 				  u64 index)
 {
-	struct btrfs_delayed_item *curr, *next;
-	int ret;
+	struct btrfs_delayed_item *curr;
+	int ret = 0;

-	if (list_empty(del_list))
-		return 0;
-
-	list_for_each_entry_safe(curr, next, del_list, readdir_list) {
+	list_for_each_entry(curr, del_list, readdir_list) {
 		if (curr->key.offset > index)
 			break;
-
-		list_del(&curr->readdir_list);
-		ret = (curr->key.offset == index);
-
-		if (refcount_dec_and_test(&curr->refs))
-			kfree(curr);
-
-		if (ret)
-			return 1;
-		else
-			continue;
+		if (curr->key.offset == index) {
+			ret = 1;
+			break;
+		}
 	}
-	return 0;
+	return ret;
 }

 /*