kernel: don't call do_exit() for PF_IO_WORKER threads

Right now we're never calling get_signal() from PF_IO_WORKER threads, but
in preparation for doing so, don't handle a fatal signal for them. The
workers have state they need to cleanup when exiting, so just return
instead of calling do_exit() on their behalf. The threads themselves will
detect a fatal signal and do proper shutdown.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

kernel/signal.c

@@ -2771,6 +2771,14 @@ bool get_signal(struct ksignal *ksig)
 			do_coredump(&ksig->info);
 		}
 
+		/*
+		 * PF_IO_WORKER threads will catch and exit on fatal signals
+		 * themselves. They have cleanup that must be performed, so
+		 * we cannot call do_exit() on their behalf.
+		 */
+		if (current->flags & PF_IO_WORKER)
+			goto out;
+
 		/*
 		 * Death signals, no core dump.
 		 */
@@ -2778,7 +2786,7 @@ bool get_signal(struct ksignal *ksig)
 		/* NOTREACHED */
 	}
 	spin_unlock_irq(&sighand->siglock);
-
+out:
 	ksig->sig = signr;
 
 	if (!(ksig->ka.sa.sa_flags & SA_EXPOSE_TAGBITS))