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bpf: Update the comments in maybe_wait_bpf_programs() 

Since commit 638e4b825d ("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@huawei.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20231211083447.1921178-1-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Hou Tao 2023-12-11 16:34:47 +08:00 committed by Alexei Starovoitov
parent b13cddf633
commit 2a0c6b41ee
1 changed files with 7 additions and 3 deletions
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10
kernel/bpf/syscall.c
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@ -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)