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* [bpf-next v5 1/3] bpf: hash map, avoid deadlock with suitable hash mask
@ 2023-01-11  9:29 tong
  2023-01-11  9:29 ` [bpf-next v5 2/3] selftests/bpf: add test case for htab map tong
  2023-01-11  9:29 ` [bpf-next v5 3/3] bpf: hash map, suppress false lockdep warning tong
  0 siblings, 2 replies; 10+ messages in thread
From: tong @ 2023-01-11  9:29 UTC (permalink / raw)
  To: bpf
  Cc: Tonghao Zhang, Alexei Starovoitov, Daniel Borkmann,
	Andrii Nakryiko, Martin KaFai Lau, Song Liu, Yonghong Song,
	John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa,
	Hou Tao

From: Tonghao Zhang <tong@infragraf.org>

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 <tong@infragraf.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Song Liu <song@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Stanislav Fomichev <sdf@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Hou Tao <houtao1@huawei.com>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Hou Tao <houtao1@huawei.com>
---
 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..66bded144377 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_t(u32, 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_t(u32, 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


^ permalink raw reply related	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2023-02-01  7:13 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2023-01-11  9:29 [bpf-next v5 1/3] bpf: hash map, avoid deadlock with suitable hash mask tong
2023-01-11  9:29 ` [bpf-next v5 2/3] selftests/bpf: add test case for htab map tong
2023-01-11  9:29 ` [bpf-next v5 3/3] bpf: hash map, suppress false lockdep warning tong
2023-01-13  1:53   ` Martin KaFai Lau
2023-01-13  2:03     ` Alexei Starovoitov
2023-01-13  2:17     ` Tonghao Zhang
2023-01-13  5:14       ` Martin KaFai Lau
2023-01-13  9:15     ` Tonghao Zhang
2023-01-15 22:51       ` Martin KaFai Lau
2023-02-01  7:12         ` Hou Tao

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