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Tue, 27 Jan 2026 22:18:07 -0800 (PST) Received: from lima-ubuntu.hz.ali.com ([47.246.98.220]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a88b4c3dd4sm11591535ad.65.2026.01.27.22.18.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jan 2026 22:18:06 -0800 (PST) From: Qing Wang To: Song Liu , Jiri Olsa , Alexei Starovoitov , peterz@infradead.org, acme@kernel.org, Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Qing Wang , syzbot+72a43cdb78469f7fbad1@syzkaller.appspotmail.com Subject: [PATCH] bpf/perf: Fix suspicious RCU usage in get_callchain_entry() Date: Wed, 28 Jan 2026 14:17:53 +0800 Message-Id: <20260128061753.1857803-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" There is a patch intended to fix suspicious RCU usage in get_callchain_entr= y(), but it is incorrect. Specifically, rcu_read_lock()/rcu_read_unlock() is not called when may_fault =3D=3D false. Previous discussion: https://lore.kernel.org/all/CAEf4BzaYL9zZN8TZyRHW3_O3vbHc7On+NSunrkDvDQx2= =3DwwyRw@mail.gmail.com/#R For perf's callchain, rcu_read_lock()/rcu_read_unlock() should be called wh= en trace_in =3D=3D false. Fixes: d4dd9775ec24 ("bpf: wire up sleepable bpf_get_stack() and bpf_get_ta= sk_stack() helpers") Reported-by: syzbot+72a43cdb78469f7fbad1@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D72a43cdb78469f7fbad1 Tested-by: syzbot+72a43cdb78469f7fbad1@syzkaller.appspotmail.com Signed-off-by: Qing Wang --- kernel/bpf/stackmap.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) 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, struc= t task_struct *task, =20 max_depth =3D stack_map_calculate_max_depth(size, elem_size, flags); =20 - if (may_fault) + if (!trace_in) rcu_read_lock(); /* need RCU for perf's callchain below */ =20 if (trace_in) { @@ -474,7 +474,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struc= t task_struct *task, } =20 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, struc= t task_struct *task, } =20 /* trace/ips should not be dereferenced after this point */ - if (may_fault) + if (!trace_in) rcu_read_unlock(); =20 if (user_build_id) --=20 2.34.1