[PATCH AUTOSEL 5.10 02/24] bpf: Annotate data races in bpf_local_storage

[Sasha Levin]

From: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>

[ Upstream commit 0a09a2f933c73dc76ab0b72da6855f44342a8903 ]

There are a few cases where hlist_node is checked to be unhashed without
holding the lock protecting its modification. In this case, one must use
hlist_unhashed_lockless to avoid load tearing and KCSAN reports. Fix
this by using lockless variant in places not protected by the lock.

Since this is not prompted by any actual KCSAN reports but only from
code review, I have not included a fixes tag.

Cc: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230221200646.2500777-4-memxor@xxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/bpf/bpf_local_storage.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index 8aaaaef99f09f..f753965726205 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -48,11 +48,21 @@ owner_storage(struct bpf_local_storage_map *smap, void *owner)
 	return map->ops->map_owner_storage_ptr(owner);
 }
 
+static bool selem_linked_to_storage_lockless(const struct bpf_local_storage_elem *selem)
+{
+	return !hlist_unhashed_lockless(&selem->snode);
+}
+
 static bool selem_linked_to_storage(const struct bpf_local_storage_elem *selem)
 {
 	return !hlist_unhashed(&selem->snode);
 }
 
+static bool selem_linked_to_map_lockless(const struct bpf_local_storage_elem *selem)
+{
+	return !hlist_unhashed_lockless(&selem->map_node);
+}
+
 static bool selem_linked_to_map(const struct bpf_local_storage_elem *selem)
 {
 	return !hlist_unhashed(&selem->map_node);
@@ -140,7 +150,7 @@ static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
 	struct bpf_local_storage *local_storage;
 	bool free_local_storage = false;
 
-	if (unlikely(!selem_linked_to_storage(selem)))
+	if (unlikely(!selem_linked_to_storage_lockless(selem)))
 		/* selem has already been unlinked from sk */
 		return;
 
@@ -167,7 +177,7 @@ void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
 	struct bpf_local_storage_map *smap;
 	struct bpf_local_storage_map_bucket *b;
 
-	if (unlikely(!selem_linked_to_map(selem)))
+	if (unlikely(!selem_linked_to_map_lockless(selem)))
 		/* selem has already be unlinked from smap */
 		return;
 
@@ -365,7 +375,7 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 		err = check_flags(old_sdata, map_flags);
 		if (err)
 			return ERR_PTR(err);
-		if (old_sdata && selem_linked_to_storage(SELEM(old_sdata))) {
+		if (old_sdata && selem_linked_to_storage_lockless(SELEM(old_sdata))) {
 			copy_map_value_locked(&smap->map, old_sdata->data,
 					      value, false);
 			return old_sdata;
-- 
2.39.2