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

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Message-ID: <fc0e2c8a-96cc-7787-6866-3802a1d5c50e@android.com>
Date:   Mon, 2 Aug 2021 18:59:03 +0000
From:   Sandeep Patil <sspatil@...roid.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 7/30/21 10:53 PM, Linus Torvalds wrote:
> 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.

Since what you merged isn't different than what I tested, I don't
expect any surprises but I will test it regardless. I will come back
if I see anything unexpected.

Thanks for the explanation about the default behavior earlier
in the thread.

- ssp