[PATCH v2 1/3] cobalt/kernel: Introduce XNDBGCTRL to block SIGINT/SIGSTOP

[Jan Kiszka <jan.kiszka@siemens.com>]

From: Jan Kiszka <jan.kiszka@siemens.com>

Setting XNDBGCTRL for a thread will prevent its migration to secondary
if only the debugging signals SIGINT or SIGSTOP are pending. Such
threads will still be able to trigger migration on other signals, such
as SIGDEBUG (watchdog), SIGCANCEL (SIGRTMIN) or synchronous SIGTRAP.

This is a building block for the debug helper feature.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 include/cobalt/uapi/kernel/thread.h |  1 +
 kernel/cobalt/posix/syscall.c       | 12 +++++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/cobalt/uapi/kernel/thread.h b/include/cobalt/uapi/kernel/thread.h
index 664def08ef..74007ac0d6 100644
--- a/include/cobalt/uapi/kernel/thread.h
+++ b/include/cobalt/uapi/kernel/thread.h
@@ -51,6 +51,7 @@
 #define XNTRAPLB  0x00100000 /**< Trap lock break (i.e. may not sleep with sched lock) */
 #define XNDEBUG   0x00200000 /**< User-level debugging enabled */
 #define XNDBGSTOP 0x00400000 /**< Stopped for synchronous debugging */
+#define XNDBGCTRL 0x00800000 /**< Thread is protected against SIGSTOP/SIGINT */
 
 /** @} */
 
diff --git a/kernel/cobalt/posix/syscall.c b/kernel/cobalt/posix/syscall.c
index cd72b22d14..d46ff103de 100644
--- a/kernel/cobalt/posix/syscall.c
+++ b/kernel/cobalt/posix/syscall.c
@@ -86,6 +86,8 @@ static void prepare_for_signal(struct task_struct *p,
 			       struct pt_regs *regs,
 			       int sysflags)
 {
+	sigset_t pending;
+	bool ignore = false;
 	int notify = 0;
 	spl_t s;
 
@@ -100,13 +102,21 @@ static void prepare_for_signal(struct task_struct *p,
 			xnthread_clear_info(thread, XNBREAK);
 		}
 		xnthread_clear_info(thread, XNKICKED);
+	} else if (xnthread_test_state(thread, XNDBGCTRL)) {
+		/* only ignore thread-specific SIGSTOP/SIGINT */
+		pending = p->pending.signal;
+		sigdelset(&pending, SIGSTOP);
+		sigdelset(&pending, SIGINT);
+		if (sigisemptyset(&pending))
+			ignore = true;
 	}
 
 	xnlock_put_irqrestore(&nklock, s);
 
 	xnthread_test_cancel();
 
-	xnthread_relax(notify, SIGDEBUG_MIGRATE_SIGNAL);
+	if (!ignore)
+		xnthread_relax(notify, SIGDEBUG_MIGRATE_SIGNAL);
 }
 
 static COBALT_SYSCALL(migrate, current, (int domain))
-- 
2.26.2