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

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Message-ID: <20250310110914.GA26382@redhat.com>
Date: Mon, 10 Mar 2025 12:09:15 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Hillf Danton <hdanton@...a.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>,
	Mateusz Guzik <mjguzik@...il.com>,
	"Sapkal, Swapnil" <swapnil.sapkal@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still
 full

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?

Oleg.