Messages in this thread | | | Date | Wed, 4 Nov 2015 12:55:38 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] ipc/msg: Implement lockless pipelined wakeups |
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On Tue, Nov 03, 2015 at 04:03:29PM +0100, Sebastian Andrzej Siewior wrote:
> - struct msg_msg *volatile r_msg; > + struct msg_msg *r_msg;
> + wake_q_add(wake_q, msr->r_tsk); > msr->r_msg = msg; > + /* > + * Rely on the implicit cmpxchg barrier from > + * wake_q_add such that we can ensure that
Davidlohr, didn't you want to make that cmpxchg_relaxed() or cmpxchg_release() ?
> + * updating msr->r_msg is the last write > + * operation: As once set, the receiver can > + * continue, and if we don't have the reference
Which seems to suggest you want to at least make that WRITE_ONCE()
> + * count from the wake_q, yet, at that point we > + * can later have a use-after-free condition and > + * bogus wakeup. > + */
And I agree with DAvidlohr that the comment is placed oddly, one would expect it between wake_q_add() and the store in question.
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