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SubjectRe: unregister_netdevice: waiting for DEV to become free (2)
Date
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> writes:

> Hello.
>
> syzbot is still reporting that bpf(BPF_MAP_UPDATE_ELEM) causes
> unregister_netdevice() to hang. It seems that commit 546ac1ffb70d25b5
> ("bpf: add devmap, a map for storing net device references") assigned
> dtab->netdev_map[i] at dev_map_update_elem() but commit 6f9d451ab1a33728
> ("xdp: Add devmap_hash map type for looking up devices by hashed index")
> forgot to assign dtab->netdev_map[idx] at __dev_map_hash_update_elem()
> when dev is newly allocated by __dev_map_alloc_node(). As far as I and
> syzbot tested, https://syzkaller.appspot.com/x/patch.diff?x=140dd206e00000
> can avoid the problem, but I don't know whether this is right location to
> assign it. Please check and fix.

Hi Tetsuo

Sorry for missing this email last week :(

I think the issue is not a missing update of dtab->netdev_map (that is
not used at all for DEVMAP_HASH), but rather that dev_map_free() is not
cleaning up properly for DEVMAP_HASH types. Could you please check if
the patch below helps?

-Toke

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 3867864cdc2f..42ccfcb38424 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -74,7 +74,7 @@ struct bpf_dtab_netdev {

struct bpf_dtab {
struct bpf_map map;
- struct bpf_dtab_netdev **netdev_map;
+ struct bpf_dtab_netdev **netdev_map; /* DEVMAP type only */
struct list_head __percpu *flush_list;
struct list_head list;

@@ -101,6 +101,12 @@ static struct hlist_head *dev_map_create_hash(unsigned int entries)
return hash;
}

+static inline struct hlist_head *dev_map_index_hash(struct bpf_dtab *dtab,
+ int idx)
+{
+ return &dtab->dev_index_head[idx & (dtab->n_buckets - 1)];
+}
+
static int dev_map_init_map(struct bpf_dtab *dtab, union bpf_attr *attr)
{
int err, cpu;
@@ -143,24 +149,22 @@ static int dev_map_init_map(struct bpf_dtab *dtab, union bpf_attr *attr)
for_each_possible_cpu(cpu)
INIT_LIST_HEAD(per_cpu_ptr(dtab->flush_list, cpu));

- dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
- sizeof(struct bpf_dtab_netdev *),
- dtab->map.numa_node);
- if (!dtab->netdev_map)
- goto free_percpu;
-
if (attr->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
dtab->dev_index_head = dev_map_create_hash(dtab->n_buckets);
if (!dtab->dev_index_head)
- goto free_map_area;
+ goto free_percpu;

spin_lock_init(&dtab->index_lock);
+ } else {
+ dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
+ sizeof(struct bpf_dtab_netdev *),
+ dtab->map.numa_node);
+ if (!dtab->netdev_map)
+ goto free_percpu;
}

return 0;

-free_map_area:
- bpf_map_area_free(dtab->netdev_map);
free_percpu:
free_percpu(dtab->flush_list);
free_charge:
@@ -228,21 +232,40 @@ static void dev_map_free(struct bpf_map *map)
cond_resched();
}

- for (i = 0; i < dtab->map.max_entries; i++) {
- struct bpf_dtab_netdev *dev;
+ if (dtab->map.map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
+ for (i = 0; i < dtab->n_buckets; i++) {
+ struct bpf_dtab_netdev *dev;
+ struct hlist_head *head;
+ struct hlist_node *next;

- dev = dtab->netdev_map[i];
- if (!dev)
- continue;
+ head = dev_map_index_hash(dtab, i);

- free_percpu(dev->bulkq);
- dev_put(dev->dev);
- kfree(dev);
+ hlist_for_each_entry_safe(dev, next, head, index_hlist) {
+ hlist_del_rcu(&dev->index_hlist);
+ free_percpu(dev->bulkq);
+ dev_put(dev->dev);
+ kfree(dev);
+ }
+ }
+
+ kfree(dtab->dev_index_head);
+ } else {
+ for (i = 0; i < dtab->map.max_entries; i++) {
+ struct bpf_dtab_netdev *dev;
+
+ dev = dtab->netdev_map[i];
+ if (!dev)
+ continue;
+
+ free_percpu(dev->bulkq);
+ dev_put(dev->dev);
+ kfree(dev);
+ }
+
+ bpf_map_area_free(dtab->netdev_map);
}

free_percpu(dtab->flush_list);
- bpf_map_area_free(dtab->netdev_map);
- kfree(dtab->dev_index_head);
kfree(dtab);
}

@@ -263,12 +286,6 @@ static int dev_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
return 0;
}

-static inline struct hlist_head *dev_map_index_hash(struct bpf_dtab *dtab,
- int idx)
-{
- return &dtab->dev_index_head[idx & (dtab->n_buckets - 1)];
-}
-
struct bpf_dtab_netdev *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
{
struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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