linux-kernel - Re: [syzbot] [perf?] WARNING: suspicious RCU usage in get_callchain

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Message-Id: <20260128035508.1840613-1-wangqing7171@gmail.com>
Date: Wed, 28 Jan 2026 11:55:08 +0800
From: Qing Wang <wangqing7171@...il.com>
To: syzbot+72a43cdb78469f7fbad1@...kaller.appspotmail.com
Cc: acme@...nel.org,
	adrian.hunter@...el.com,
	alexander.shishkin@...ux.intel.com,
	irogers@...gle.com,
	jolsa@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	mark.rutland@....com,
	mingo@...hat.com,
	namhyung@...nel.org,
	peterz@...radead.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [perf?] WARNING: suspicious RCU usage in get_callchain_entry

#syz test

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index da3d328f5c15..f97d4aa9d038 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -460,7 +460,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 
 	max_depth = stack_map_calculate_max_depth(size, elem_size, flags);
 
-	if (may_fault)
+	if (!trace_in)
 		rcu_read_lock(); /* need RCU for perf's callchain below */
 
 	if (trace_in) {
@@ -474,7 +474,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 	}
 
 	if (unlikely(!trace) || trace->nr < skip) {
-		if (may_fault)
+		if (!trace_in)
 			rcu_read_unlock();
 		goto err_fault;
 	}
@@ -494,7 +494,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 	}
 
 	/* trace/ips should not be dereferenced after this point */
-	if (may_fault)
+	if (!trace_in)
 		rcu_read_unlock();
 
 	if (user_build_id)