From: Oleg Nesterov <oleg@redhat.com>
Date: Wed, 26 Jun 2024 19:10:17 +0000 (+0200)
Subject: get_task_mm: check PF_KTHREAD lockless
X-Git-Tag: v6.11-rc1~85^2~112
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8ac5dc66599c;p=thirdparty%2Flinux.git

get_task_mm: check PF_KTHREAD lockless

Nowadays PF_KTHREAD is sticky and it was never protected by ->alloc_lock.
Move the PF_KTHREAD check outside of task_lock() section to make this code
more understandable.

Link: https://lkml.kernel.org/r/20240626191017.GA20031@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/kernel/fork.c b/kernel/fork.c
index 99076dbe27d83..279efadabbf22 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1536,14 +1536,13 @@ struct mm_struct *get_task_mm(struct task_struct *task)
 {
 	struct mm_struct *mm;
 
+	if (task->flags & PF_KTHREAD)
+		return NULL;
+
 	task_lock(task);
 	mm = task->mm;
-	if (mm) {
-		if (task->flags & PF_KTHREAD)
-			mm = NULL;
-		else
-			mmget(mm);
-	}
+	if (mm)
+		mmget(mm);
 	task_unlock(task);
 	return mm;
 }