linux-kernel - Re: [PATCH 1/1] fs: pipe: wakeup readers everytime new data written is to pipe

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Date:   Fri, 30 Jul 2021 15:53:34 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Sandeep Patil <sspatil@...roid.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable <stable@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/1] fs: pipe: wakeup readers everytime new data written
 is to pipe

On Fri, Jul 30, 2021 at 12:23 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I'll mull it over a bit more, but whatever I'll do I'll do before rc4
> and mark it for stable.

Ok, I ended up committing the minimal possible change (and fixing up
the comment above it).

It's very much *not* the original behavior either, but that original
behavior was truly insane ("wake up for each hunk written"), and I'm
trying to at least keep the kernel code from doing actively stupid
things.

Since that old patch of mine worked for your test-case, then clearly
that realm-core library didn't rely on _that_ kind of insane internal
kernel implementation details exposed as semantics. So The minimal
patch basically says "each write() system call wil do at least one
wake-up, whether really necessary or not".

I also intentionally kept the read side untouched, in that there
apparently still isn't a case that would need the confused semantics
for read events.

End result: the commit message is a lot bigger than the patch, with
most of it being trying to explain the background.

I've pushed it out as commit 3a34b13a88ca ("pipe: make pipe writes
always wake up readers"). Holler if you notice anything odd remaining.

              Linus