Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still full

[Hillf Danton]

On Wed, 5 Mar 2025 12:44:34 +0100 Oleg Nesterov <oleg@xxxxxxxxxx>
> On 03/05, Hillf Danton wrote:
> > See the loop in  ___wait_event(),
> >
> > 	for (;;) {
> > 		prepare_to_wait_event();
> >
> > 		// flip
> > 		if (condition)
> > 			break;
> >
> > 		schedule();
> > 	}
> >
> > After wakeup, waiter will sleep again if condition flips false on the waker
> > side before waiter checks condition, even if condition is atomic, no?
> 
> Yes, but in this case pipe_full() == true is correct, this writer can
> safely sleep.
> 
No, because no reader is woken up before sleep to make pipe not full.