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vhost: Take a reference on the task in struct vhost_task. 

vhost_task_create() creates a task and keeps a reference to its
task_struct. That task may exit early via a signal and its task_struct
will be released.
A pending vhost_task_wake() will then attempt to wake the task and
access a task_struct which is no longer there.

Acquire a reference on the task_struct while creating the thread and
release the reference while the struct vhost_task itself is removed.
If the task exits early due to a signal, then the vhost_task_wake() will
still access a valid task_struct. The wake is safe and will be skipped
in this case.

Fixes: f9010dbdce ("fork, vhost: Use CLONE_THREAD to fix freezer/ps regression")
Reported-by: Sean Christopherson <seanjc@google.com>
Closes: https://lore.kernel.org/all/aKkLEtoDXKxAAWju@google.com/
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Message-Id: <20250918181144.Ygo8BZ-R@linutronix.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sebastian Andrzej Siewior 2025-09-18 20:11:44 +02:00 committed by Michael S. Tsirkin
parent e430451613
commit afe16653e0
1 changed files with 2 additions and 1 deletions
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3
kernel/vhost_task.c
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@ -100,6 +100,7 @@ void vhost_task_stop(struct vhost_task *vtsk)
* freeing it below. * freeing it below.
*/ */
wait_for_completion(&vtsk->exited); wait_for_completion(&vtsk->exited);
put_task_struct(vtsk->task);
kfree(vtsk); kfree(vtsk);
} }
EXPORT_SYMBOL_GPL(vhost_task_stop); EXPORT_SYMBOL_GPL(vhost_task_stop);
@ -148,7 +149,7 @@ struct vhost_task *vhost_task_create(bool (*fn)(void *),
return ERR_CAST(tsk); return ERR_CAST(tsk);
} }
vtsk->task = tsk; vtsk->task = get_task_struct(tsk);
return vtsk; return vtsk;
} }
EXPORT_SYMBOL_GPL(vhost_task_create); EXPORT_SYMBOL_GPL(vhost_task_create);