netdev - Re: [PATCH v4 bpf-next 2/6] bpf: prevent deadlock from recursive bpf_task_storage

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Date:   Tue, 23 Feb 2021 12:06:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        kernel-team@...com
Subject: Re: [PATCH v4 bpf-next 2/6] bpf: prevent deadlock from recursive
 bpf_task_storage_[get|delete]

On Mon, Feb 22, 2021 at 05:20:10PM -0800, Song Liu wrote:
> BPF helpers bpf_task_storage_[get|delete] could hold two locks:
> bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling
> these helpers from fentry/fexit programs on functions in bpf_*_storage.c
> may cause deadlock on either locks.
> 
> Prevent such deadlock with a per cpu counter, bpf_task_storage_busy, which
> is similar to bpf_prog_active. We need this counter to be global, because

So bpf_prog_active is one of the biggest turds around, and now you're
making it worse ?!