btrfs: use refcount_inc_not_zero in kill_all_nodes

BugLink: https://bugs.launchpad.net/bugs/1857158
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index a6226cd6063c78dd0194c4c368698047da84b0a2..6082880b433b326f315990566b627f406dbaf875 100644 (file)
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1931,12 +1931,19 @@ 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]);
                }