netdev - RE: [PATCH 1/4] fs: Implement close-on-fork

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Date:   Wed, 22 Apr 2020 16:02:49 +0000
From:   "Karstens, Nate" <Nate.Karstens@...min.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Alexander Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Arnd Bergmann <arnd@...db.de>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-alpha@...r.kernel.org" <linux-alpha@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Laight <David.Laight@...lab.com>,
        Changli Gao <xiaosuo@...il.com>
Subject: RE: [PATCH 1/4] fs: Implement close-on-fork

> It's not safe to call system() from a threaded app.  That's all.  It's right there in the DESCRIPTION:

That is true, but that description is missing from both the Linux man page and the glibc documentation (https://www.gnu.org/software/libc/manual/html_mono/libc.html#Running-a-Command). It seems like a minor point that won't be noticed until it causes a problem, and problems are rare enough they might go unnoticed for a while. We have removed system() from our application, but we're also concerned that libraries we integrate will use system() without our knowledge.

-----Original Message-----
From: Matthew Wilcox <willy@...radead.org>
Sent: Wednesday, April 22, 2020 10:44
To: Karstens, Nate <Nate.Karstens@...min.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>; Jeff Layton <jlayton@...nel.org>; J. Bruce Fields <bfields@...ldses.org>; Arnd Bergmann <arnd@...db.de>; Richard Henderson <rth@...ddle.net>; Ivan Kokshaysky <ink@...assic.park.msu.ru>; Matt Turner <mattst88@...il.com>; James E.J. Bottomley <James.Bottomley@...senpartnership.com>; Helge Deller <deller@....de>; David S. Miller <davem@...emloft.net>; Jakub Kicinski <kuba@...nel.org>; linux-fsdevel@...r.kernel.org; linux-arch@...r.kernel.org; linux-alpha@...r.kernel.org; linux-parisc@...r.kernel.org; sparclinux@...r.kernel.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org; David Laight <David.Laight@...lab.com>; Changli Gao <xiaosuo@...il.com>
Subject: Re: [PATCH 1/4] fs: Implement close-on-fork

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On Wed, Apr 22, 2020 at 03:36:09PM +0000, Karstens, Nate wrote:
> There was some skepticism about whether our practice of
> closing/reopening sockets was advisable. Regardless, it does expose
> what I believe to be something that was overlooked in the forking
> process model. We posted two solutions to the Austin Group defect tracker:

I don't think it was "overlooked" at all.  It's not safe to call system() from a threaded app.  That's all.  It's right there in the DESCRIPTION:

   The system() function need not be thread-safe.
https://pubs.opengroup.org/onlinepubs/9699919799/functions/system.html

> Ultimately the Austin Group felt that close-on-fork was the preferred
> approach. I think it's also worth pointing that out Solaris reportedly
> has this feature
> (https://www.mail-archive.com/austin-group-l@opengroup.org/msg05359.html).

I am perplexed that the Austin Group thought this was a good idea.

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