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 1e956ff9acd3..788f6971d32d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1569,7 +1569,7 @@ 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 1654d6e7c148..ebf143aa427b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7792,16 +7792,17 @@ 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;
 }
 
-- 
2.47.0