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| author | Martin KaFai Lau <martin.lau@kernel.org> | 2022-10-25 21:45:19 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-10-26 09:11:46 +0300 |
| commit | e8b02296a6b8d07de752d6157d863a642117bcd3 (patch) | |
| tree | 4c91db052a526edd1deba8b1c3509bc117345dec /kernel/bpf/bpf_local_storage.c | |
| parent | 6d65500c34d897329ed1be0fd3c4014ec52cd473 (diff) | |
| download | linux-e8b02296a6b8d07de752d6157d863a642117bcd3.tar.xz | |
bpf: Avoid taking spinlock in bpf_task_storage_get if potential deadlock is detected
bpf_task_storage_get() does a lookup and optionally inserts
new data if BPF_LOCAL_STORAGE_GET_F_CREATE is present.
During lookup, it will cache the lookup result and caching requires to
acquire a spinlock. When potential deadlock is detected (by the
bpf_task_storage_busy pcpu-counter added in
commit bc235cdb423a ("bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete]")),
the current behavior is returning NULL immediately to avoid deadlock. It is
too pessimistic. This patch will go ahead to do a lookup (which is a
lockless operation) but it will avoid caching it in order to avoid
acquiring the spinlock.
When lookup fails to find the data and BPF_LOCAL_STORAGE_GET_F_CREATE
is set, an insertion is needed and this requires acquiring a spinlock.
This patch will still return NULL when a potential deadlock is detected.
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20221025184524.3526117-5-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf/bpf_local_storage.c')
| -rw-r--r-- | kernel/bpf/bpf_local_storage.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c index 9dc6de1cf185..781d14167140 100644 --- a/kernel/bpf/bpf_local_storage.c +++ b/kernel/bpf/bpf_local_storage.c @@ -242,6 +242,7 @@ void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool use_trace_rcu) __bpf_selem_unlink_storage(selem, use_trace_rcu); } +/* If cacheit_lockit is false, this lookup function is lockless */ struct bpf_local_storage_data * bpf_local_storage_lookup(struct bpf_local_storage *local_storage, struct bpf_local_storage_map *smap, |