linux-kernel - Re: [GIT PULL] HID fixes

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Message-ID: <CAHk-=wji9frEf=nkfBmekhZs7QofyhDuT7_Lqt=kkjEZVAktzA@mail.gmail.com>
Date:   Thu, 9 Jan 2020 15:41:31 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: Re: [GIT PULL] HID fixes

On Thu, Jan 9, 2020 at 3:36 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Now, good source code presumably notices EPOLLERR and handles it. So
> it _shouldn't_ matter what the kernel does if an error occurs. I
> haven't checked what people _actually_ do, tnough. I worry sometimes
> that user space just looks at EPOLLIN sees it not being set, and gets
> stuck in a busy loop polling in case of errors.

Googling around for it, I find this, for example:

    https://github.com/scylladb/seastar/issues/309

and yes, I think that's technically a user space bug, but it's very
much an example of this: they expect to get errors through read() or
write() calls, and get confused when poll() does not say that the fd
is readable or writable.

I don't know how common this is, but it didn't take a _lot_ of
googling for me to find that one..

           Linus