bpf: Send signals asynchronously if !preemptible

BPF programs can execute in all kinds of contexts and when a program
running in a non-preemptible context uses the bpf_send_signal() kfunc,
it will cause issues because this kfunc can sleep.
Change `irqs_disabled()` to `!preemptible()`.

Reported-by: [email protected]
Closes: https://lore.kernel.org/all/[email protected]/
Fixes: 1bc7896 ("bpf: Fix deadlock with rq_lock in bpf_send_signal()")
Signed-off-by: Puranjay Mohan <[email protected]>
Acked-by: Yonghong Song <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: puranjaymohan

kernel/trace/bpf_trace.c

@@ -842,7 +842,7 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type, struct task_struc
 	if (unlikely(is_global_init(task)))
 		return -EPERM;
 
-	if (irqs_disabled()) {
+	if (!preemptible()) {
 		/* Do an early check on signal validity. Otherwise,
 		 * the error is lost in deferred irq_work.
 		 */