Re: [PATCH bpf-next v6 1/6] bpf: Add sleepable support for raw tracepoint programs

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:

> On Tue, Mar 24, 2026 at 12:03 PM Mykyta Yatsenko
> <mykyta.yatsenko5@gmail.com> wrote:
>>
>> From: Mykyta Yatsenko <yatsenko@meta.com>
>>
>> Rework __bpf_trace_run() to support sleepable BPF programs by using
>> explicit RCU flavor selection, following the uprobe_prog_run() pattern.
>>
>> For sleepable programs, use rcu_read_lock_tasks_trace() for lifetime
>> protection and add a might_fault() annotation. For non-sleepable
>> programs, use the regular rcu_read_lock(). Replace the combined
>> rcu_read_lock_dont_migrate() with separate rcu_read_lock()/
>> migrate_disable() calls, since sleepable programs need
>> rcu_read_lock_tasks_trace() instead of rcu_read_lock().
>>
>> Remove the preempt_disable_notrace/preempt_enable_notrace pair from
>> the faultable tracepoint BPF probe wrapper in bpf_probe.h, since
>> migration protection and RCU locking are now handled per-program
>> inside __bpf_trace_run().
>>
>> This prepares the runtime execution path for both BTF-based raw
>> tracepoints (tp_btf) and classic raw tracepoints (raw_tp) to support
>> sleepable BPF programs on faultable tracepoints (e.g. syscall
>> tracepoints). The verifier changes to allow loading sleepable
>> programs are in a subsequent patch.
>>
>> Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
>> ---
>>  include/trace/bpf_probe.h |  2 --
>>  kernel/trace/bpf_trace.c  | 21 ++++++++++++++++++---
>>  2 files changed, 18 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
>> index 9391d54d3f12..d1de8f9aa07f 100644
>> --- a/include/trace/bpf_probe.h
>> +++ b/include/trace/bpf_probe.h
>> @@ -58,9 +58,7 @@ static notrace void                                                   \
>>  __bpf_trace_##call(void *__data, proto)                                        \
>>  {                                                                      \
>>         might_fault();                                                  \
>> -       preempt_disable_notrace();                                      \
>>         CONCATENATE(bpf_trace_run, COUNT_ARGS(args))(__data, CAST_TO_U64(args));        \
>> -       preempt_enable_notrace();                                       \
>>  }
>>
>>  #undef DECLARE_EVENT_SYSCALL_CLASS
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index 0b040a417442..35ed53807cfd 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -2072,11 +2072,18 @@ void bpf_put_raw_tracepoint(struct bpf_raw_event_map *btp)
>>  static __always_inline
>>  void __bpf_trace_run(struct bpf_raw_tp_link *link, u64 *args)
>>  {
>> +       struct srcu_ctr __percpu *scp = NULL;
>>         struct bpf_prog *prog = link->link.prog;
>> +       bool sleepable = prog->sleepable;
>>         struct bpf_run_ctx *old_run_ctx;
>>         struct bpf_trace_run_ctx run_ctx;
>>
>> -       rcu_read_lock_dont_migrate();
>> +       if (sleepable)
>> +               scp = rcu_read_lock_tasks_trace();
>> +       else
>> +               rcu_read_lock();
>> +
>> +       migrate_disable();
>
> Pls don't sacrifice performance just to have common migrate_disable path.
>
>>         if (unlikely(!bpf_prog_get_recursion_context(prog))) {
>>                 bpf_prog_inc_misses_counter(prog);
>>                 goto out;
>> @@ -2085,12 +2092,20 @@ void __bpf_trace_run(struct bpf_raw_tp_link *link, u64 *args)
>>         run_ctx.bpf_cookie = link->cookie;
>>         old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx);
>>
>> -       (void) bpf_prog_run(prog, args);
>> +       if (sleepable)
>> +               might_fault();
>
> why?
> might_fault() is there __BPF_DECLARE_TRACE_SYSCALL.
>
Agreed, thanks.
> pw-bot: cr