Commit 9f907439 authored by Tonghao Zhang's avatar Tonghao Zhang Committed by Martin KaFai Lau
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bpf: hash map, avoid deadlock with suitable hash mask 



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.

Fixes: 20b6cc34 ("bpf: Avoid hashtab deadlock with map_locked")
Signed-off-by: default avatarTonghao 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: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarHou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20230111092903.92389-1-tong@infragraf.org


Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
parent e7895f01

kernel/bpf/hashtab.c

+2 −2
Original line number Diff line number Diff line
@@ -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();