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pid: use READ_ONCE() in pid_alive()

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KCSAN reports pid_alive() reading task->thread_pid while it gets cleared
under tasklist_lock. The check only cares about NULL, so READ_ONCE() and
WRITE_ONCE() are enough.

Reported-by: syzbot+c382ee653fd70f5cf1bb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c382ee653fd70f5cf1bb
Signed-off-by: Babanpreet Singh <bbnpreetsingh@gmail.com>
Link: https://patch.msgid.link/20261002012141.7-1-bbnpreetsingh@gmail.com
Acked-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Babanpreet Singh 2026-10-02 01:21:41 +00:00 committed by Christian Brauner
parent 2ec5a07094
commit 12e19bba68
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
2 changed files with 2 additions and 2 deletions
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2
include/linux/pid.h
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@ -273,7 +273,7 @@ static inline pid_t task_tgid_nr(struct task_struct *tsk)
*/
static inline int pid_alive(const struct task_struct *p)
{
return p->thread_pid != NULL;
return READ_ONCE(p->thread_pid) != NULL;
}
static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)

2
kernel/pid.c
View File

@ -411,7 +411,7 @@ static void __change_pid(struct pid **pids, struct task_struct *task,
pid = *pid_ptr;
hlist_del_rcu(&task->pid_links[type]);
*pid_ptr = new;
WRITE_ONCE(*pid_ptr, new);
for (tmp = PIDTYPE_MAX; --tmp >= 0; )
if (pid_has_task(pid, tmp))