[PATCH v4 32/39] perf: Remove get_perf_callchain() 'crosstask' argument

Josh Poimboeuf
2025-01-22T02:32:25Z

get_perf_callchain() doesn't support cross-task unwinding, so it doesn't
make much sense to have 'crosstask' as an argument.

Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
include/linux/perf_event.h | 2 +-
kernel/bpf/stackmap.c | 12 ++++--------
kernel/events/callchain.c | 6 +-----
kernel/events/core.c | 9 +++++----
4 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 4c8ff7258c6a..1563dc2cd979 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1590,7 +1590,7 @@ extern void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct p
extern void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs);
extern struct perf_callchain_entry *
get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
- u32 max_stack, bool crosstask, bool add_mark);
+ u32 max_stack, bool add_mark);
extern int get_callchain_buffers(int max_stack);
extern void put_callchain_buffers(void);
extern struct perf_callchain_entry *get_callchain_entry(int *rctx);
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index ec3a57a5fba1..ee9701337912 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -314,8 +314,7 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
if (max_depth > sysctl_perf_event_max_stack)
max_depth = sysctl_perf_event_max_stack;

- trace = get_perf_callchain(regs, kernel, user, max_depth,
- false, false);
+ trace = get_perf_callchain(regs, kernel, user, max_depth, false);

if (unlikely(!trace))
/* couldn't fetch the stack trace */
@@ -430,10 +429,8 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
if (task && user && !user_mode(regs))
goto err_fault;

- /* get_perf_callchain does not support crosstask user stack walking
- * but returns an empty stack instead of NULL.
- */
- if (crosstask && user) {
+ /* get_perf_callchain() does not support crosstask stack walking */
+ if (crosstask) {
err = -EOPNOTSUPP;
goto clear;
}
@@ -451,8 +448,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
else if (kernel && task)
trace = get_callchain_entry_for_task(task, max_depth);
else
- trace = get_perf_callchain(regs, kernel, user, max_depth,
- crosstask, false);
+ trace = get_perf_callchain(regs, kernel, user, max_depth,false);

if (unlikely(!trace) || trace->nr < skip) {
if (may_fault)
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 83834203e144..655fb25a725b 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -217,7 +217,7 @@ static void fixup_uretprobe_trampoline_entries(struct perf_callchain_entry *entr

struct perf_callchain_entry *
get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
- u32 max_stack, bool crosstask, bool add_mark)
+ u32 max_stack, bool add_mark)
{
struct perf_callchain_entry *entry;
struct perf_callchain_entry_ctx ctx;
@@ -248,9 +248,6 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
}

if (regs) {
- if (crosstask)
- goto exit_put;
-
if (add_mark)
perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);

@@ -260,7 +257,6 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
}
}

-exit_put:
put_callchain_entry(rctx);

return entry;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ebe457bacf96..99f0f28feeb5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7793,16 +7793,17 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
{
bool kernel = !event->attr.exclude_callchain_kernel;
bool user = !event->attr.exclude_callchain_user;
- /* Disallow cross-task user callchains. */
- bool crosstask = event->ctx->task && event->ctx->task != current;
const u32 max_stack = event->attr.sample_max_stack;
struct perf_callchain_entry *callchain;

if (!kernel && !user)
return &__empty_callchain;

- callchain = get_perf_callchain(regs, kernel, user,
- max_stack, crosstask, true);
+ /* Disallow cross-task callchains. */
+ if (event->ctx->task && event->ctx->task != current)
+ return &__empty_callchain;
+
+ callchain = get_perf_callchain(regs, kernel, user, max_stack, true);
return callchain ?: &__empty_callchain;
}

--
2.48.1