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bpf: Avoid changing callchain in bpf_get_stack_pe

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There's no need to modify the trace object bpf_get_stack_pe, we just
need to pass the needed callchain length in separate argument.

This way we can have callchain pointers const and remove the trace->nr
modification and restoration.

Assisted-by: Codex:GPT-5.5

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260803210149.296496-12-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2026-08-03 23:01:48 +02:00 committed by Andrii Nakryiko
parent b1a47b2708
commit 347c1d722e
1 changed files with 15 additions and 21 deletions
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36
kernel/bpf/stackmap.c
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@ -661,7 +661,7 @@ const struct bpf_func_proto bpf_get_stackid_proto = {
.arg3_type = ARG_ANYTHING,
};
static __u64 count_kernel_ip(struct perf_callchain_entry *trace)
static __u64 count_kernel_ip(const struct perf_callchain_entry *trace)
{
__u64 nr_kernel = 0;
@ -741,15 +741,15 @@ const struct bpf_func_proto bpf_get_stackid_proto_pe = {
.arg3_type = ARG_ANYTHING,
};
static u32 callchain_store(struct perf_callchain_entry *trace, void *buf,
u32 elem_size, u64 flags)
static u32 callchain_store(const struct perf_callchain_entry *trace, u32 trace_nr,
void *buf, u32 elem_size, u64 flags)
{
bool user_build_id = flags & BPF_F_USER_BUILD_ID;
u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
u32 trace_nr, copy_len;
u64 *ips;
const u64 *ips;
u32 copy_len;
trace_nr = trace->nr - skip;
trace_nr = trace_nr - skip;
copy_len = trace_nr * elem_size;
ips = trace->ip + skip;
@ -833,7 +833,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
goto err_fault;
}
trace_nr = callchain_store(trace, buf, elem_size, flags);
trace_nr = callchain_store(trace, trace->nr, buf, elem_size, flags);
/* trace should not be dereferenced after this point */
if (may_fault)
@ -935,8 +935,8 @@ const struct bpf_func_proto bpf_get_task_stack_sleepable_proto = {
.arg4_type = ARG_ANYTHING,
};
static int __bpf_get_stack_pe(struct perf_callchain_entry *trace, void *buf, u32 size,
u64 flags)
static int __bpf_get_stack_pe(const struct perf_callchain_entry *trace, u32 trace_nr,
void *buf, u32 size, u64 flags)
{
bool user_build_id = flags & BPF_F_USER_BUILD_ID;
u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
@ -952,12 +952,12 @@ static int __bpf_get_stack_pe(struct perf_callchain_entry *trace, void *buf, u32
return -EINVAL;
max_depth = stack_map_calculate_max_depth(size, elem_size, flags);
trace->nr = min_t(u32, trace->nr, max_depth);
trace_nr = min_t(u32, trace_nr, max_depth);
if (trace->nr < skip)
if (trace_nr < skip)
return -EFAULT;
nr_trace = callchain_store(trace, buf, elem_size, flags);
nr_trace = callchain_store(trace, trace_nr, buf, elem_size, flags);
return callchain_finalize(buf, size, nr_trace, elem_size, flags, false /* !may_fault */);
}
@ -965,8 +965,8 @@ BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx,
void *, buf, u32, size, u64, flags)
{
struct pt_regs *regs = (struct pt_regs *)(ctx->regs);
const struct perf_callchain_entry *trace;
struct perf_event *event = ctx->event;
struct perf_callchain_entry *trace;
bool kernel, user;
int err = -EINVAL;
__u64 nr_kernel;
@ -989,13 +989,7 @@ BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx,
nr_kernel = count_kernel_ip(trace);
if (kernel) {
__u64 nr = trace->nr;
trace->nr = nr_kernel;
err = __bpf_get_stack_pe(trace, buf, size, flags);
/* restore nr */
trace->nr = nr;
err = __bpf_get_stack_pe(trace, nr_kernel, buf, size, flags);
} else { /* user */
u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
@ -1003,7 +997,7 @@ BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx,
if (skip > BPF_F_SKIP_FIELD_MASK)
goto clear;
flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
err = __bpf_get_stack_pe(trace, buf, size, flags);
err = __bpf_get_stack_pe(trace, trace->nr, buf, size, flags);
}
clear: