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From: Martin KaFai Lau <kafai@fb.com>
To: Song Liu <songliubraving@fb.com>
Cc: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <ast@kernel.org>,
	<daniel@iogearbox.net>, <kernel-team@fb.com>,
	<peterz@infradead.org>
Subject: Re: [PATCH v6 bpf-next 2/6] bpf: prevent deadlock from recursive bpf_task_storage_[get|delete]
Date: Thu, 25 Feb 2021 16:01:57 -0800	[thread overview]
Message-ID: <20210226000157.yoe7hbzocavn5udk@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210225234319.336131-3-songliubraving@fb.com>

On Thu, Feb 25, 2021 at 03:43:15PM -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. We
> need this counter to be global, because the two locks here belong to two
> different objects: bpf_local_storage_map and bpf_local_storage. If we
> pick one of them as the owner of the counter, it is still possible to
> trigger deadlock on the other lock. For example, if bpf_local_storage_map
> owns the counters, it cannot prevent deadlock on bpf_local_storage->lock
> when two maps are used.
Acked-by: Martin KaFai Lau <kafai@fb.com>

  reply	other threads:[~2021-02-26  0:03 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-25 23:43 [PATCH v6 bpf-next 0/6] bpf: enable task local storage for tracing programs Song Liu
2021-02-25 23:43 ` [PATCH v6 bpf-next 1/6] " Song Liu
2021-02-25 23:43 ` [PATCH v6 bpf-next 2/6] bpf: prevent deadlock from recursive bpf_task_storage_[get|delete] Song Liu
2021-02-26  0:01   ` Martin KaFai Lau [this message]
2021-02-25 23:43 ` [PATCH v6 bpf-next 3/6] selftests/bpf: add non-BPF_LSM test for task local storage Song Liu
2021-02-25 23:43 ` [PATCH v6 bpf-next 4/6] selftests/bpf: test deadlock from recursive bpf_task_storage_[get|delete] Song Liu
2021-02-25 23:43 ` [PATCH v6 bpf-next 5/6] bpf: runqslower: prefer using local vmlimux to generate vmlinux.h Song Liu
2021-02-25 23:43 ` [PATCH v6 bpf-next 6/6] bpf: runqslower: use task local storage Song Liu
2021-02-26  0:03 ` [PATCH v6 bpf-next 0/6] bpf: enable task local storage for tracing programs Martin KaFai Lau
2021-02-26 20:03   ` Alexei Starovoitov

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