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From: Josef Bacik <>
To: Alexei Starovoitov <>,
Subject: Re: [PATCH v3 bpf-next 2/5] bpf: Introduce sleepable BPF programs
Date: Thu, 27 Aug 2020 21:01:01 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 8/27/20 6:01 PM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <>
> Introduce sleepable BPF programs that can request such property for themselves
> via BPF_F_SLEEPABLE flag at program load time. In such case they will be able
> to use helpers like bpf_copy_from_user() that might sleep. At present only
> fentry/fexit/fmod_ret and lsm programs can request to be sleepable and only
> when they are attached to kernel functions that are known to allow sleeping.
> The non-sleepable programs are relying on implicit rcu_read_lock() and
> migrate_disable() to protect life time of programs, maps that they use and
> per-cpu kernel structures used to pass info between bpf programs and the
> kernel. The sleepable programs cannot be enclosed into rcu_read_lock().
> migrate_disable() maps to preempt_disable() in non-RT kernels, so the progs
> should not be enclosed in migrate_disable() as well. Therefore
> rcu_read_lock_trace is used to protect the life time of sleepable progs.
> There are many networking and tracing program types. In many cases the
> 'struct bpf_prog *' pointer itself is rcu protected within some other kernel
> data structure and the kernel code is using rcu_dereference() to load that
> program pointer and call BPF_PROG_RUN() on it. All these cases are not touched.
> Instead sleepable bpf programs are allowed with bpf trampoline only. The
> program pointers are hard-coded into generated assembly of bpf trampoline and
> synchronize_rcu_tasks_trace() is used to protect the life time of the program.
> The same trampoline can hold both sleepable and non-sleepable progs.
> When rcu_read_lock_trace is held it means that some sleepable bpf program is
> running from bpf trampoline. Those programs can use bpf arrays and preallocated
> hash/lru maps. These map types are waiting on programs to complete via
> synchronize_rcu_tasks_trace();
> Updates to trampoline now has to do synchronize_rcu_tasks_trace() and
> synchronize_rcu_tasks() to wait for sleepable progs to finish and for
> trampoline assembly to finish.
> This is the first step of introducing sleepable progs. Eventually dynamically
> allocated hash maps can be allowed and networking program types can become
> sleepable too.
> Signed-off-by: Alexei Starovoitov <>
> Acked-by: Andrii Nakryiko <>

Reviewed-by: Josef Bacik <>



  parent reply	other threads:[~2020-08-28  1:01 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-27 22:01 [PATCH v3 bpf-next 0/5] bpf: Introduce minimal support for sleepable progs Alexei Starovoitov
2020-08-27 22:01 ` [PATCH v3 bpf-next 1/5] mm/error_inject: Fix allow_error_inject function signatures Alexei Starovoitov
2020-08-27 23:58   ` Josef Bacik
2020-08-28 20:27   ` Daniel Borkmann
2020-08-29 22:47     ` Alexei Starovoitov
2020-08-27 22:01 ` [PATCH v3 bpf-next 2/5] bpf: Introduce sleepable BPF programs Alexei Starovoitov
2020-08-27 22:28   ` KP Singh
2020-08-28  1:01   ` Josef Bacik [this message]
2020-08-31 14:51   ` Björn Töpel
2020-08-31 16:26     ` Alexei Starovoitov
2020-08-27 22:01 ` [PATCH v3 bpf-next 3/5] bpf: Add bpf_copy_from_user() helper Alexei Starovoitov
2020-08-27 22:29   ` KP Singh
2020-08-27 22:01 ` [PATCH v3 bpf-next 4/5] libbpf: support sleepable progs Alexei Starovoitov
2020-08-27 22:01 ` [PATCH v3 bpf-next 5/5] selftests/bpf: Add sleepable tests Alexei Starovoitov
2020-08-29 22:13   ` Yonghong Song
2020-08-29 22:38     ` Alexei Starovoitov
2020-08-30  0:22       ` Yonghong Song
2020-08-31 16:56         ` Alexei Starovoitov
2020-08-28 20:10 ` [PATCH v3 bpf-next 0/5] bpf: Introduce minimal support for sleepable progs Daniel Borkmann

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