From: Hou Tao <houtao1@xxxxxxxxxx>
Since commit 638e4b825d52 ("bpf: Allows per-cpu maps and map-in-map in
sleepable programs"), sleepable BPF program can also use map-in-map, but
maybe_wait_bpf_programs() doesn't handle it accordingly. The main reason
is that using synchronize_rcu_tasks_trace() to wait for the completions
of these sleepable BPF programs may incur a very long delay and
userspace may think it is hung, so the wait for sleepable BPF programs
is skipped. Update the comments in maybe_wait_bpf_programs() to reflect
the reason.
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
v2:
* Don't handle sleepable BPF programs due to the potential long delay
* Update the comments in maybe_wait_bpf_programs() accordingly
v1: https://lore.kernel.org/bpf/20231208102355.2628918-8-houtao@xxxxxxxxxxxxxxx/
* Handle sleepable BPF programs in maybe_wait_bpf_programs()
kernel/bpf/syscall.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0496b78b80f7..3fcf7741146a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -142,9 +142,13 @@ static u32 bpf_map_value_size(const struct bpf_map *map)
static void maybe_wait_bpf_programs(struct bpf_map *map)
{
- /* Wait for any running BPF programs to complete so that
- * userspace, when we return to it, knows that all programs
- * that could be running use the new map value.
+ /* Wait for any running non-sleepable BPF programs to complete so that
+ * userspace, when we return to it, knows that all non-sleepable
+ * programs that could be running use the new map value. For sleepable
+ * BPF programs, synchronize_rcu_tasks_trace() should be used to wait
+ * for the completions of these programs, but considering the waiting
+ * time can be very long and userspace may think it will hang forever,
+ * so don't handle sleepable BPF programs now.
*/
if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS ||
map->map_type == BPF_MAP_TYPE_ARRAY_OF_MAPS)
--
2.29.2
