Date:   Fri, 17 Mar 2023 10:16:36 -0700
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
To:     starmiku1207184332@gmail.com
Cc:     ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        martin.lau@linux.dev, song@kernel.org, yhs@fb.com,
        john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
        haoluo@google.com, jolsa@kernel.org, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org, baijiaju1990@outlook.com
Subject: Re: [PATCH v2] kernel: bpf: stackmap: fix a possible sleep-in-atomic
 bug in bpf_mmap_unlock_get_irq_work()
Message-ID: <20230317171636.ftelyp6ty7mgo4rt@dhcp-172-26-102-232.dhcp.thefacebook.com>
References: <20230317035227.22293-1-starmiku1207184332@gmail.com>
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On Fri, Mar 17, 2023 at 03:52:27AM +0000, starmiku1207184332@gmail.com wrote:
> context because of its possible sleep operation. However, mmap_read_unlock()
> is unsafely called in a preempt disabled context when spin_lock() or
> rcu_read_lock() has been called.

Why is that unsafe?
See __up_read(). It's doing preempt_disable().


> -	if (irqs_disabled()) {
> +	if (in_atomic() || irqs_disabled()) {

We cannot do this. It will significantly hurt stack traces with build_id.