linux-kernel - [PATCH RFC 02/10] perf: Remove get_perf

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Date:   Wed,  8 Nov 2023 16:41:07 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Indu Bhagat <indu.bhagat@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        linux-toolchains@...r.kernel.org
Subject: [PATCH RFC 02/10] perf: Remove get_perf_callchain() 'crosstask' argument

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

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 include/linux/perf_event.h | 2 +-
 kernel/bpf/stackmap.c      | 5 ++---
 kernel/events/callchain.c  | 6 +-----
 kernel/events/core.c       | 8 ++++----
 4 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f4b05954076c..2d8fa253b9df 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1534,7 +1534,7 @@ 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 b0b0fbff7c18..e4827ca5378d 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -294,8 +294,7 @@ 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 */
@@ -421,7 +420,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 		trace = get_callchain_entry_for_task(task, max_depth);
 	else
 		trace = get_perf_callchain(regs, kernel, user, max_depth,
-					   false, false);
+					   false);
 	if (unlikely(!trace))
 		goto err_fault;
 
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 1e135195250c..aa5f9d11c28d 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -178,7 +178,7 @@ put_callchain_entry(int rctx)
 
 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;
@@ -209,9 +209,6 @@ 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);
 
@@ -219,7 +216,6 @@ 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 b0d62df7df4e..5e41a3b70bcd 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7592,16 +7592,16 @@ 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;
 
+	/* Disallow cross-task user callchains. */
+	user &= !event->ctx->task || event->ctx->task == current;
+
 	if (!kernel && !user)
 		return &__empty_callchain;
 
-	callchain = get_perf_callchain(regs, kernel, user,
-				       max_stack, crosstask, true);
+	callchain = get_perf_callchain(regs, kernel, user, max_stack, true);
 	return callchain ?: &__empty_callchain;
 }
 
-- 
2.41.0