linux-kernel - [PATCH 10/17] signal: Only set JOBCTL_WILL

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Date: Tue, 18 Jun 2024 23:09:44 -0500
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,  Tejun Heo <tj@...nel.org>,
  linux-kernel@...r.kernel.org
Subject: [PATCH 10/17] signal: Only set JOBCTL_WILL_EXIT if it is not
 already set


The various code paths that set JOBCTL_WILL_EXIT optimize away setting
JOBCTL_WILL_EXIT and calling signal_wake_up based on different
conditions.  If the task has already committed itself to exiting by
setting JOBCTL_WILL_EXIT, setting JOBCTL_WILL_EXIT will accomplish
nothing.  So instead of using any of the original conditions only set
JOBCTL_WILL_EXIT when JOBCTL_WILL_EXIT is not set.

Additionally skip task_clear_jobctl_pending once JOBCTL_WILL_EXIT has
been set as task_set_jobctl_pending won't set any pending bits after
that.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/coredump.c   |  4 ++--
 kernel/exit.c   |  5 ++++-
 kernel/signal.c | 21 +++++++++++++--------
 3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index f3e363fa09a3..bcef41ec69a9 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -371,8 +371,8 @@ static int zap_process(struct task_struct *start, int exit_code)
 	start->signal->group_stop_count = 0;
 
 	for_each_thread(start, t) {
-		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
-		if (!(t->flags & PF_POSTCOREDUMP)) {
+		if (!(t->jobctl & JOBCTL_WILL_EXIT)) {
+			task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 			t->jobctl |= JOBCTL_WILL_EXIT;
 			signal_wake_up(t, 1);
 		}
diff --git a/kernel/exit.c b/kernel/exit.c
index 0059c60946a3..73eb3afbf083 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -801,7 +801,10 @@ static void synchronize_group_exit(struct task_struct *tsk, long code)
 	struct signal_struct *signal = tsk->signal;
 
 	spin_lock_irq(&sighand->siglock);
-	tsk->jobctl |= JOBCTL_WILL_EXIT;
+	if (!(tsk->jobctl & JOBCTL_WILL_EXIT)) {
+		task_clear_jobctl_pending(tsk, JOBCTL_PENDING_MASK);
+		tsk->jobctl |= JOBCTL_WILL_EXIT;
+	}
 	signal->quick_threads--;
 	if ((signal->quick_threads == 0) &&
 	    !(signal->flags & SIGNAL_GROUP_EXIT)) {
diff --git a/kernel/signal.c b/kernel/signal.c
index 12e552a35848..341717c6cc97 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -911,8 +911,10 @@ static bool prepare_signal(int sig, struct task_struct *p, bool force)
 		if (signal->core_state && (sig == SIGKILL)) {
 			struct task_struct *dumper =
 				signal->core_state->dumper.task;
-			dumper->jobctl |= JOBCTL_WILL_EXIT;
-			signal_wake_up(dumper, 1);
+			if (!(dumper->jobctl & JOBCTL_WILL_EXIT)) {
+				dumper->jobctl |= JOBCTL_WILL_EXIT;
+				signal_wake_up(dumper, 1);
+			}
 		}
 		/*
 		 * The process is in the middle of dying, drop the signal.
@@ -1054,9 +1056,11 @@ static void complete_signal(int sig, struct task_struct *p, enum pid_type type)
 			signal->group_exit_code = sig;
 			signal->group_stop_count = 0;
 			__for_each_thread(signal, t) {
-				task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
-				t->jobctl |= JOBCTL_WILL_EXIT;
-				signal_wake_up(t, 1);
+				if (!(t->jobctl & JOBCTL_WILL_EXIT)) {
+					task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
+					t->jobctl |= JOBCTL_WILL_EXIT;
+					signal_wake_up(t, 1);
+				}
 			}
 			return;
 		}
@@ -1378,12 +1382,13 @@ int zap_other_threads(struct task_struct *p)
 	p->signal->group_stop_count = 0;
 
 	for_other_threads(p, t) {
-		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 		count++;
 
-		/* Don't bother with already dead threads */
-		if (t->exit_state)
+		/* Only bother with threads that might be alive */
+		if (t->jobctl & JOBCTL_WILL_EXIT)
 			continue;
+
+		task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
 		t->jobctl |= JOBCTL_WILL_EXIT;
 		signal_wake_up(t, 1);
 	}
-- 
2.41.0