diff options
| author | Namhyung Kim <namhyung@kernel.org> | 2022-03-14 11:20:41 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-04-08 14:40:43 +0200 |
| commit | 90805175a206f784b6a77f16f07b07f6803e286b (patch) | |
| tree | 5e8c5678a5c620499622b74a20c5d32801cdedee /include | |
| parent | 86489492e87680c9c1c13a1a73ee278c13ecbab6 (diff) | |
bpf: Adjust BPF stack helper functions to accommodate skip > 0
commit ee2a098851bfbe8bcdd964c0121f4246f00ff41e upstream.
Let's say that the caller has storage for num_elem stack frames. Then,
the BPF stack helper functions walk the stack for only num_elem frames.
This means that if skip > 0, one keeps only 'num_elem - skip' frames.
This is because it sets init_nr in the perf_callchain_entry to the end
of the buffer to save num_elem entries only. I believe it was because
the perf callchain code unwound the stack frames until it reached the
global max size (sysctl_perf_event_max_stack).
However it now has perf_callchain_entry_ctx.max_stack to limit the
iteration locally. This simplifies the code to handle init_nr in the
BPF callstack entries and removes the confusion with the perf_event's
__PERF_SAMPLE_CALLCHAIN_EARLY which sets init_nr to 0.
Also change the comment on bpf_get_stack() in the header file to be
more explicit what the return value means.
Fixes: c195651e565a ("bpf: add bpf_get_stack helper")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/30a7b5d5-6726-1cc2-eaee-8da2828a9a9c@oracle.com
Link: https://lore.kernel.org/bpf/20220314182042.71025-1-namhyung@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Based-on-patch-by: Eugene Loh <eugene.loh@oracle.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/uapi/linux/bpf.h | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 762bf87c26a3..baa2867dc236 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -2163,8 +2163,8 @@ union bpf_attr { * * # sysctl kernel.perf_event_max_stack=<new value> * Return - * A non-negative value equal to or less than *size* on success, - * or a negative error in case of failure. + * The non-negative copied *buf* length equal to or less than + * *size* on success, or a negative error in case of failure. * * long bpf_skb_load_bytes_relative(const void *skb, u32 offset, void *to, u32 len, u32 start_header) * Description @@ -3448,8 +3448,8 @@ union bpf_attr { * * # sysctl kernel.perf_event_max_stack=<new value> * Return - * A non-negative value equal to or less than *size* on success, - * or a negative error in case of failure. + * The non-negative copied *buf* length equal to or less than + * *size* on success, or a negative error in case of failure. * * long bpf_load_hdr_opt(struct bpf_sock_ops *skops, void *searchby_res, u32 len, u64 flags) * Description |