Re: [PATCH v3] ipc/mqueue: Avoid relying on a stack reference past its expiry

Hi Varad,

On 5/7/21 3:38 PM, Varad Gautam wrote:

@@ -1005,11 +1022,9 @@ static inline void __pipelined_op(struct wake_q_head *wake_q, struct ext_wait_queue *this) { list_del(&this->list);

• get_task_struct(this->task);

• wake_q_add(wake_q, this->task); /* see MQ_BARRIER for purpose/pairing */ smp_store_release(&this->state, STATE_READY);

• wake_q_add_safe(wake_q, this->task); }

/* pipelined_send() - send a message directly to the task waiting in

First, I was too fast: I had assumed that wake_q_add() before smp_store_release() would be a potential lost wakeup.

As __pipelined_op() is called within spin_lock(&info->lock), and as wq_sleep() will reread this->state after acquiring spin_lock(&info->lock), I do not see a bug anymore.

But I don't like the change: Why should ipc/*.c differ from kernel/futex.c?

--

Manfred