• Alexei Starovoitov's avatar
    bpf: Introduce sleepable BPF programs · 1e6c62a8
    Alexei Starovoitov authored
    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: default avatarAlexei Starovoitov <ast@kernel.org>
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
    Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
    Acked-by: default avatarKP Singh <kpsingh@google.com>
    Link: https://lore.kernel.org/bpf/20200827220114.69225-3-alexei.starovoitov@gmail.com
    1e6c62a8
syscall.c 99.9 KB