From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: "Feng Yang" <yangfeng59949@163.com>, <song@kernel.org>,
<jolsa@kernel.org>, <ihor.solodrai@linux.dev>,
<kpsingh@kernel.org>, <matt@bobrowski.net>,
<daniel@iogearbox.net>, <andrii@kernel.org>, <eddyz87@gmail.com>,
<memxor@gmail.com>, <martin.lau@linux.dev>,
<yonghong.song@linux.dev>, <emil@etsalapatis.com>,
<rostedt@goodmis.org>, <mhiramat@kernel.org>,
<mathieu.desnoyers@efficios.com>
Cc: <bpf@vger.kernel.org>, <linux-trace-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 bpf-next] bpf: Fix suspicious RCU usage for sleepable bpf_get_stack()
Date: Tue, 03 Nov 2026 03:03:02 +0000 [thread overview]
Message-ID: <DML8PRKSQ4ZX.2A8Q5SC26RO6Q@gmail.com> (raw)
In-Reply-To: <20261102073714.1103088-1-yangfeng59949@163.com>
On Sun, Nov 01, 2026 at 11:37 PM Feng Yang <yangfeng59949@163.com> wrote:
> Route these paths to bpf_get_stack_sleepable() and mark the new protos
> might_sleep, since build_id_parse() may fault in file data for
> BPF_F_USER_STACK | BPF_F_USER_BUILD_ID. Sleepable programs that call
> bpf_get_stack() from inside a bpf_rcu_read_lock() region are now rejected
> by the verifier, which is the correct behavior for a helper that can
> sleep.
That's a new feature. It's not a fix for the splat.
Andrii's point in v1 is about build IDs. That's a good reason for this
patch, but the splat needs Songsen's patch anyway:
https://lore.kernel.org/bpf/20261028121859.994-1-yangsongsen@insta360.com/
Songsen's patch this patch
------------------------------------ --------------- -------------
splat in sleepable progs fixed fixed
splat in bpf_wq, task_work callbacks fixed still there
build ID when the page is paged out no yes
progs that load today all load some rejected
Row 2: the callback is sleepable, but its prog is not.
bpf_wq_work() rcu_read_lock_trace() only
callback_fn() prog->sleepable == false
bpf_get_task_stack() may_fault == false
__bpf_get_stack() no rcu_read_lock()
get_callchain_entry() rcu_dereference(): splat
Row 4: sleepable fentry, lsm, iter, syscall and tracepoint progs that
call bpf_get_stack() under bpf_rcu_read_lock() or bpf_preempt_disable()
load fine today. With this patch the verifier rejects them.
It does so even when flags don't have BPF_F_USER_BUILD_ID.
Pls respin it as a feature, with a new subject and commit log
and a selftest.
pw-bot: cr
next prev parent reply other threads:[~2026-11-03 3:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-02 7:37 [PATCH v2 bpf-next] bpf: Fix suspicious RCU usage for sleepable bpf_get_stack() Feng Yang
2026-11-02 8:14 ` bot+bpf-ci
2026-11-03 3:03 ` Alexei Starovoitov [this message]
2026-11-03 9:02 ` Feng Yang
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