Commit f7d32765 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
Browse files

bpf: Have __bpf_trace_run() use rcu_read_lock_dont_migrate() 

In order to switch the protection of tracepoint callbacks from
preempt_disable() to srcu_read_lock_fast() the BPF callback from
tracepoints needs to have migration prevention as the BPF programs expect
to stay on the same CPU as they execute. Put together the RCU protection
with migration prevention and use rcu_read_lock_dont_migrate() in
__bpf_trace_run(). This will allow tracepoints callbacks to be
preemptible.

Link: https://lore.kernel.org/all/CAADnVQKvY026HSFGOsavJppm3-Ajm-VsLzY-OeFUe+BaKMRnDg@mail.gmail.com/

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20260126231256.335034877@kernel.org


Suggested-by: default avatarAlexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 16718274

kernel/trace/bpf_trace.c

+2 −3
Original line number Diff line number Diff line
@@ -2062,7 +2062,7 @@ void __bpf_trace_run(struct bpf_raw_tp_link *link, u64 *args) 
	struct bpf_run_ctx *old_run_ctx;

	struct bpf_trace_run_ctx run_ctx;



	cant_sleep();

	rcu_read_lock_dont_migrate();

	if (unlikely(this_cpu_inc_return(*(prog->active)) != 1)) {

		bpf_prog_inc_misses_counter(prog);

		goto out;
@@ -2071,13 +2071,12 @@ 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);



	rcu_read_lock();

	(void) bpf_prog_run(prog, args);

	rcu_read_unlock();



	bpf_reset_run_ctx(old_run_ctx);

out:

	this_cpu_dec(*(prog->active));

	rcu_read_unlock_migrate();

}



#define UNPACK(...)			__VA_ARGS__