bpf: Send signals asynchronously if !preemptible

JIRA: https://issues.redhat.com/browse/RHEL-85486
JIRA: https://issues.redhat.com/browse/RHEL-81243

CVE: CVE-2025-21728

Conflicts: Context change due to missing commit 6280cf7 ("bpf:
Implement bpf_send_signal_task() kfunc").

commit 87c5441
Author: Puranjay Mohan <[email protected]>
Date:   Wed Jan 15 10:36:47 2025 +0000

    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]>

Signed-off-by: Jerome Marchand <[email protected]>

Author: jeromemarchand

kernel/trace/bpf_trace.c

@@ -832,7 +832,7 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type)
 	if (unlikely(is_global_init(current)))
 		return -EPERM;
 
-	if (irqs_disabled()) {
+	if (!preemptible()) {
 		/* Do an early check on signal validity. Otherwise,
 		 * the error is lost in deferred irq_work.
 		 */