linux-kernel - [tip: perf/core] perf: Have get_perf_callchain() return NULL if crosstask and user are set

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Message-ID: <175627712187.1920.14304918617440613309.tip-bot2@tip-bot2>
Date: Wed, 27 Aug 2025 06:45:21 -0000
From: "tip-bot2 for Josh Poimboeuf" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Josh Poimboeuf <jpoimboe@...nel.org>,
 "Steven Rostedt (Google)" <rostedt@...dmis.org>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf: Have get_perf_callchain() return NULL if
 crosstask and user are set

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     153f9e74dec230f2e070e16fa061bc7adfd2c450
Gitweb:        https://git.kernel.org/tip/153f9e74dec230f2e070e16fa061bc7adfd2c450
Author:        Josh Poimboeuf <jpoimboe@...nel.org>
AuthorDate:    Wed, 20 Aug 2025 14:03:40 -04:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 26 Aug 2025 09:51:12 +02:00

perf: Have get_perf_callchain() return NULL if crosstask and user are set

get_perf_callchain() doesn't support cross-task unwinding for user space
stacks, have it return NULL if both the crosstask and user arguments are
set.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20250820180428.426423415@kernel.org
---
 kernel/events/callchain.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index b0f5bd2..cd0e3fc 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -224,6 +224,10 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
 	struct perf_callchain_entry_ctx ctx;
 	int rctx, start_entry_idx;
 
+	/* crosstask is not supported for user stacks */
+	if (crosstask && user && !kernel)
+		return NULL;
+
 	entry = get_callchain_entry(&rctx);
 	if (!entry)
 		return NULL;
@@ -240,7 +244,7 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
 		perf_callchain_kernel(&ctx, regs);
 	}
 
-	if (user) {
+	if (user && !crosstask) {
 		if (!user_mode(regs)) {
 			if  (current->mm)
 				regs = task_pt_regs(current);
@@ -249,9 +253,6 @@ 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);
 
@@ -261,7 +262,6 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
 		}
 	}
 
-exit_put:
 	put_callchain_entry(rctx);
 
 	return entry;