release/5.2.31/btrfs-use-refcount_inc_not_zero-in-kill_all_nodes.patch

From d40d395439824bf802183b4a569c5d3a4c7f7617 Mon Sep 17 00:00:00 2001
From: Josef Bacik <josef@toxicpanda.com>
Date: Thu, 26 Sep 2019 08:29:32 -0400
Subject: [PATCH] btrfs: use refcount_inc_not_zero in kill_all_nodes

commit baf320b9d531f1cfbf64c60dd155ff80a58b3796 upstream.

We hit the following warning while running down a different problem

[ 6197.175850] ------------[ cut here ]------------
[ 6197.185082] refcount_t: underflow; use-after-free.
[ 6197.194704] WARNING: CPU: 47 PID: 966 at lib/refcount.c:190 refcount_sub_and_test_checked+0x53/0x60
[ 6197.521792] Call Trace:
[ 6197.526687]  __btrfs_release_delayed_node+0x76/0x1c0
[ 6197.536615]  btrfs_kill_all_delayed_nodes+0xec/0x130
[ 6197.546532]  ? __btrfs_btree_balance_dirty+0x60/0x60
[ 6197.556482]  btrfs_clean_one_deleted_snapshot+0x71/0xd0
[ 6197.566910]  cleaner_kthread+0xfa/0x120
[ 6197.574573]  kthread+0x111/0x130
[ 6197.581022]  ? kthread_create_on_node+0x60/0x60
[ 6197.590086]  ret_from_fork+0x1f/0x30
[ 6197.597228] ---[ end trace 424bb7ae00509f56 ]---

This is because the free side drops the ref without the lock, and then
takes the lock if our refcount is 0.  So you can have nodes on the tree
that have a refcount of 0.  Fix this by zero'ing out that element in our
temporary array so we don't try to kill it again.

CC: stable@vger.kernel.org # 4.14+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ add comment ]
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 6858a05606dd..8235ac0db4b1 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1948,12 +1948,19 @@ void btrfs_kill_all_delayed_nodes(struct btrfs_root *root)
 		}
 
 		inode_id = delayed_nodes[n - 1]->inode_id + 1;
-
-		for (i = 0; i < n; i++)
-			refcount_inc(&delayed_nodes[i]->refs);
+		for (i = 0; i < n; i++) {
+			/*
+			 * Don't increase refs in case the node is dead and
+			 * about to be removed from the tree in the loop below
+			 */
+			if (!refcount_inc_not_zero(&delayed_nodes[i]->refs))
+				delayed_nodes[i] = NULL;
+		}
 		spin_unlock(&root->inode_lock);
 
 		for (i = 0; i < n; i++) {
+			if (!delayed_nodes[i])
+				continue;
 			__btrfs_kill_delayed_node(delayed_nodes[i]);
 			btrfs_release_delayed_node(delayed_nodes[i]);
 		}
-- 
2.7.4