On 03/10, Hillf Danton wrote: > > On Mon, 10 Mar 2025 12:09:15 +0100 Oleg Nesterov > > On 03/10, Hillf Danton wrote: > > > On Sun, 9 Mar 2025 18:02:55 +0100 Oleg Nesterov > > > > > > > > So (again, in this particular case) we could apply the patch below > > > > on top of Linus's tree. > > > > > > > > So, with or without these changes, the writer should be woken up at > > > > step-03 in your scenario. > > > > > > > Fine, before checking my scenario once more, feel free to pinpoint the > > > line number where writer is woken up, with the change below applied. > > > > 381 if (wake_writer) > > ==> 382 wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM); > > 383 if (wake_next_reader) > > 384 wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM); > > 385 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT); > > 386 if (ret > 0) > > 387 file_accessed(filp); > > 388 return ret; > > > > line 382, no? > > > Yes, but how is the wait loop at line-370 broken? > > 360 } > 361 mutex_unlock(&pipe->mutex); > 362 > 363 BUG_ON(wake_writer); > 364 /* > 365 * But because we didn't read anything, at this point we can > 366 * just return directly with -ERESTARTSYS if we're interrupted, > 367 * since we've done any required wakeups and there's no need > 368 * to mark anything accessed. And we've dropped the lock. > 369 */ > 370 if (wait_event_interruptible_exclusive(pipe->rd_wait, pipe_readable(pipe)) < 0) > 371 return -ERESTARTSYS; Hmm. I don't understand you, again. OK, once some writer writes at least one byte (this will make the pipe_empty() condition false) and wakes this reader up. If you meant something else, say, if you referred to you previous scenario, please clarify your question. Oleg.
