From: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
The deadlock still may occur while accessed in NMI and non-NMI
context. Because in NMI, we still may access the same bucket but with
different map_locked index.
For example, on the same CPU, .max_entries = 2, we update the hash map,
with key = 4, while running bpf prog in NMI nmi_handle(), to update
hash map with key = 20, so it will have the same bucket index but have
different map_locked index.
To fix this issue, using min mask to hash again.
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Hao Luo <haoluo@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Hou Tao <houtao1@xxxxxxxxxx>
---
kernel/bpf/hashtab.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 5aa2b5525f79..8b25036a8690 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -152,7 +152,7 @@ static inline int htab_lock_bucket(const struct bpf_htab *htab,
{
unsigned long flags;
- hash = hash & HASHTAB_MAP_LOCK_MASK;
+ hash = hash & min(HASHTAB_MAP_LOCK_MASK, htab->n_buckets -1);
preempt_disable();
if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
@@ -171,7 +171,7 @@ static inline void htab_unlock_bucket(const struct bpf_htab *htab,
struct bucket *b, u32 hash,
unsigned long flags)
{
- hash = hash & HASHTAB_MAP_LOCK_MASK;
+ hash = hash & min(HASHTAB_MAP_LOCK_MASK, htab->n_buckets -1);
raw_spin_unlock_irqrestore(&b->raw_lock, flags);
__this_cpu_dec(*(htab->map_locked[hash]));
preempt_enable();
--
2.27.0
