From: Peter Zijlstra <peterz@infradead.org>
To: Qing Wang <wangqing7171@gmail.com>
Cc: syzbot+72a43cdb78469f7fbad1@syzkaller.appspotmail.com,
acme@kernel.org, adrian.hunter@intel.com,
alexander.shishkin@linux.intel.com, irogers@google.com,
jolsa@kernel.org, linux-kernel@vger.kernel.org,
linux-perf-users@vger.kernel.org, mark.rutland@arm.com,
mingo@redhat.com, namhyung@kernel.org,
syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [perf?] WARNING: suspicious RCU usage in get_callchain_entry
Date: Wed, 28 Jan 2026 09:52:00 +0100 [thread overview]
Message-ID: <20260128085200.GE3372621@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260128035508.1840613-1-wangqing7171@gmail.com>
On Wed, Jan 28, 2026 at 11:55:08AM +0800, Qing Wang wrote:
> #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)
>
This is just papering over more bugs. There was a series out there
somewhere trying to fix up this code, let me see if I can find it in
this shitshow called an inbox :/
next prev parent reply other threads:[~2026-01-28 8:52 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-30 10:49 [syzbot] [perf?] WARNING: suspicious RCU usage in get_callchain_entry syzbot
2026-01-28 3:52 ` Qing Wang
2026-01-28 4:26 ` syzbot
2026-01-28 3:55 ` Qing Wang
2026-01-28 4:50 ` syzbot
2026-01-28 8:52 ` Peter Zijlstra [this message]
2026-01-28 9:15 ` Qing Wang
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