xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

bpf: Adjust BPF stack helper functions to accommodate skip > 0

Browse Source 
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: c195651e56 ("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>
This commit is contained in:
Namhyung Kim
2022-03-14 11:20:41 -07:00
committed by Greg Kroah-Hartman
parent 86489492e8
commit 90805175a2
2 changed files with 28 additions and 36 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
include/uapi/linux/bpf.h
View File

@@ -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