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.
Signed-off-by: Josef Bacik <jo...@toxicpanda.com>
---
v2->v3:
- always git show after a revision kids, to make sure your new code still makes
sense with the original code, not your previous version.
fs/btrfs/delayed-inode.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 1f7f39b10bd0..ac71615a480c 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1949,12 +1949,15 @@ 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++) {
+ 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]);
}
--
2.21.0
