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bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete]

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BPF helpers bpf_task_storage_[get|delete] could hold two locks:
bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling
these helpers from fentry/fexit programs on functions in bpf_*_storage.c
may cause deadlock on either locks.

Prevent such deadlock with a per cpu counter, bpf_task_storage_busy. We
need this counter to be global, because the two locks here belong to two
different objects: bpf_local_storage_map and bpf_local_storage. If we
pick one of them as the owner of the counter, it is still possible to
trigger deadlock on the other lock. For example, if bpf_local_storage_map
owns the counters, it cannot prevent deadlock on bpf_local_storage->lock
when two maps are used.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210225234319.336131-3-songliubraving@fb.com
This commit is contained in:
Song Liu
2021-02-25 15:43:15 -08:00
committed by Alexei Starovoitov
parent a10787e6d5
commit bc235cdb42
5 changed files with 65 additions and 12 deletions
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3
include/linux/bpf_local_storage.h
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@@ -126,7 +126,8 @@ bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
struct bpf_local_storage_map *smap,
bool cacheit_lockit);
void bpf_local_storage_map_free(struct bpf_local_storage_map *smap);
void bpf_local_storage_map_free(struct bpf_local_storage_map *smap,
int __percpu *busy_counter);
int bpf_local_storage_map_check_btf(const struct bpf_map *map,
const struct btf *btf,