signal: print comm and exe name on fatal signals

Make the print-fatal-signals message more useful by printing the comm
and the exe name for the process which received the fatal signal:

Before:

 potentially unexpected fatal signal 4
 potentially unexpected fatal signal 11

After:

 buggy-program: pool: potentially unexpected fatal signal 4
 some-daemon: gdbus: potentially unexpected fatal signal 11

comm used to be present but was removed in commit 681a90ffe8
("arc, print-fatal-signals: reduce duplicated information") because it's
also included as part of the later stack trace.  Having the comm as part
of the main "unexpected fatal..." print is rather useful though when
analysing logs, and the exe name is also valuable as shown in the
examples above where the comm ends up having some generic name like
"pool".

[akpm@linux-foundation.org: don't include linux/file.h twice]
Link: https://lkml.kernel.org/r/20230707-fatal-comm-v1-1-400363905d5e@axis.com
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vineet Gupta <vgupta@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kernel/signal.c

@@ -22,6 +22,7 @@
 #include <linux/sched/cputime.h>
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/mm.h>
 #include <linux/proc_fs.h>
 #include <linux/tty.h>
 #include <linux/binfmts.h>
@@ -1260,7 +1261,17 @@ int send_signal_locked(int sig, struct kernel_siginfo *info,
 static void print_fatal_signal(int signr)
 {
 	struct pt_regs *regs = task_pt_regs(current);
-	pr_info("potentially unexpected fatal signal %d.\n", signr);
+	struct file *exe_file;
+
+	exe_file = get_task_exe_file(current);
+	if (exe_file) {
+		pr_info("%pD: %s: potentially unexpected fatal signal %d.\n",
+			exe_file, current->comm, signr);
+		fput(exe_file);
+	} else {
+		pr_info("%s: potentially unexpected fatal signal %d.\n",
+			current->comm, signr);
+	}
 
 #if defined(__i386__) && !defined(__arch_um__)
 	pr_info("code at %08lx: ", regs->ip);