Re: [PATCH 0/6] tracing/ring-buffer: Fix wakeup of ring buffer waiters

[Linus Torvalds <torvalds@linux-foundation.org>]

On Fri, 8 Mar 2024 at 13:33, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> There's two layers:
>
> 1) the ring buffer has the above simple producer / consumer.
>    Where the wake ups can happen at the point of where the buffer has
>    the amount filled that the consumer wants to start consuming with.
>
> 2) The tracing layer; Here on close of a file, the consumers need to be
>    woken up and not wait again. And just take whatever was there to finish
>    reading.
>
>    There's also another case that the ioctl() just kicks the current
>    readers out, but doesn't care about new readers.

But that's the beauty of just using the wait_event() model.

Just add that "exit" condition to the condition.

So the above "complexity" is *literally* just changing the

                  (new = atomic_read_acquire(&my->seq)) != old

condition to

                  should_exit ||
                  (new = atomic_read_acquire(&my->seq)) != old

(replace "should_exit" with whatever that condition is, of course) and
the wait_event() logic will take care of the rest.

             Linus