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kthread: Annotate lockless to_kthread() flags access

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do_exit() calls synchronize_group_exit(), which modifies task->flags
under sighand->siglock:

	tsk->flags |= PF_POSTCOREDUMP;

The sanity check in to_kthread() reads the same flags word without
holding that lock:

	WARN_ON(!(k->flags & PF_KTHREAD));

PF_KTHREAD is set once when the task becomes a kthread and is never
cleared for the lifetime of the task.  Since PF_KTHREAD is immutable,
the check does not depend on synchronization with updates to other
bits in task->flags.

Use READ_ONCE() to annotate the intentional lockless access.

Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
Link: https://patch.msgid.link/20260920070750.2871923-1-kunwu.chan@gmail.com
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Kunwu Chan 2026-09-20 15:07:50 +08:00 committed by Christian Brauner
parent 8421a62085
commit fd00a46e36
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1 changed files with 1 additions and 1 deletions
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2
kernel/kthread.c
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@ -81,7 +81,7 @@ enum KTHREAD_BITS {
static inline struct kthread *to_kthread(struct task_struct *k)
{
WARN_ON(!(k->flags & PF_KTHREAD));
WARN_ON(!(READ_ONCE(k->flags) & PF_KTHREAD));
return k->worker_private;
}