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 we're unconditionally grabbing a ref to every node, but
there could be nodes with a 0 refcount. Fix this to instead use
refcount_inc_not_zero() and only process the list for the nodes we get a
refcount on.
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
fs/btrfs/delayed-inode.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 1f7f39b10bd0..320503750896 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1936,7 +1936,7 @@ void btrfs_kill_all_delayed_nodes(struct btrfs_root *root)
{
u64 inode_id = 0;
struct btrfs_delayed_node *delayed_nodes[8];
- int i, n;
+ int i, n, count;
while (1) {
spin_lock(&root->inode_lock);
@@ -1948,13 +1948,16 @@ void btrfs_kill_all_delayed_nodes(struct btrfs_root *root)
break;
}
- inode_id = delayed_nodes[n - 1]->inode_id + 1;
-
- for (i = 0; i < n; i++)
- refcount_inc(&delayed_nodes[i]->refs);
+ count = 0;
+ for (i = 0; i < n; i++) {
+ if (!refcount_inc_not_zero(&delayed_nodes[i]->refs))
+ break;
+ count++;
+ }
+ inode_id = delayed_nodes[count - 1]->inode_id + 1;
spin_unlock(&root->inode_lock);
- for (i = 0; i < n; i++) {
+ for (i = 0; i < count; i++) {
__btrfs_kill_delayed_node(delayed_nodes[i]);
btrfs_release_delayed_node(delayed_nodes[i]);
}
--
2.21.0
