linux-kernel - Re: May close() return any error code?

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Message-ID: <20150729144511.GA11233@dtor-ws>
Date:	Wed, 29 Jul 2015 07:45:11 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Takashi Iwai <tiwai@...e.de>, Al Viro <viro@...iv.linux.org.uk>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Dr. Werner Fink" <werner@...e.de>
Subject: Re: May close() return any error code?

HI Takashi,

On Wed, Jul 29, 2015 at 12:46:59PM +0200, Takashi Iwai wrote:
> Hi,
> 
> while debugging a problem of X and gdm with the old systemd-210, we
> encountered a sudden death of systemd-logind, and this turned out to
> be an unexpected errno from close().  The close() call for input
> devices returns ENODEV error.  The logind in systemd-210 treats this
> error code as fatal, triggers assert() and eventually kills itself.
> The details are found in an openSUSE bugzilla thread:
>   https://bugzilla.opensuse.org/show_bug.cgi?id=939571
> 
> This seems coming from evdev_flush().  As there is no fd leak, it's no
> big problem per se.  But, now the question is whether returning such
> an error code is correct behavior at all.  At least, it doesn't seem
> defined in POSIX:
>   http://pubs.opengroup.org/onlinepubs/009695399/functions/close.html

Hmm, if I checked the right version of the code close_nointr_nofail()
expects only 0 as the return code so even if we change the kernel to
use more conforming -EIO instead of -ENODEV systemd will still die...

The question is whether we really need to propagate return value from
f_op->flush() up to userspace in filp_close(). Why don't we ask Al?

Thanks.

-- 
Dmitry
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