FAILED: patch "[PATCH] taskstats: Cleanup the use of task->exit_code" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1b5a42d9c85f0e731f01c8d1129001fd8531a8a0 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Mon, 3 Jan 2022 11:32:36 -0600
Subject: [PATCH] taskstats: Cleanup the use of task->exit_code

In the function bacct_add_task the code reading task->exit_code was introduced in commit f3cef7a99469 ("[PATCH] csa: basic accounting over taskstats"), and it is not entirely clear what the taskstats interface is trying to return as only returning the exit_code of the first task in a process doesn't make a lot of sense.

As best as I can figure the intent is to return task->exit_code after a task exits. The field is returned with per task fields, so the exit_code of the entire process is not wanted. Only the value of the first task is returned so this is not a useful way to get the per task ptrace stop code. The ordinary case of returning this value is returning after a task exits, which also precludes use for getting a ptrace value.

It is common to for the first task of a process to also be the last task of a process so this field may have done something reasonable by accident in testing.

Make ac_exitcode a reliable per task value by always returning it for every exited task.

Setting ac_exitcode in a sensible mannter makes it possible to continue to provide this value going forward.

index f00de83d0246..1d261fbe367b 100644
@@ -38,11 +38,10 @@ void bacct_add_tsk(struct user_namespace *user_ns,
 	stats->ac_btime = clamp_t(time64_t, btime, 0, U32_MAX);
 	stats->ac_btime64 = btime;
 
-	if (thread_group_leader(tsk)) {
+	if (tsk->flags & PF_EXITING)
 		stats->ac_exitcode = tsk->exit_code;
-		if (tsk->flags & PF_FORKNOEXEC)
-			stats->ac_flag |= AFORK;
-	}
+	if (thread_group_leader(tsk) && (tsk->flags & PF_FORKNOEXEC))
+		stats->ac_flag |= AFORK;
 	if (tsk->flags & PF_SUPERPRIV)
 		stats->ac_flag |= ASU;
 	if (tsk->flags & PF_DUMPCORE)