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From: Rich Felker <dalias@libc.org>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
	linux-kernel@vger.kernel.org, libc-alpha@sourceware.org,
	alistair23@gmail.com, ebiederm@xmission.com, arnd@arndb.de,
	torvalds@linux-foundation.org, adhemerval.zanella@linaro.org,
	fweimer@redhat.com, palmer@sifive.com, macro@wdc.com,
	zongbox@gmail.com, akpm@linux-foundation.org,
	viro@zeniv.linux.org.uk, hpa@zytor.com
Subject: Re: [PATCH v3 1/1] waitid: Add support for waiting for the current process group
Date: Wed, 14 Aug 2019 12:55:01 -0400
Message-ID: <20190814165501.GJ9017@brightrain.aerifal.cx> (raw)
In-Reply-To: <20190814163443.6odsksff4jbta7be@wittgenstein>

On Wed, Aug 14, 2019 at 06:34:44PM +0200, Christian Brauner wrote:
> On Wed, Aug 14, 2019 at 06:15:17PM +0200, Christian Brauner wrote:
> > On Wed, Aug 14, 2019 at 06:09:17PM +0200, Oleg Nesterov wrote:
> > > On 08/14, Christian Brauner wrote:
> > > >
> > > > and a signal could come in between the system call that
> > > > retrieved the process gorup and the call to waitid that changes the
> > >                         ^^^^^
> > > > current process group.
> > > 
> > > I noticed this typo only because I spent 2 minutes or more trying to
> > > understand this sentence ;) But yes, a signal handler or another thread
> > 
> > I'll try to rewrite it. :)
> 
> Ok, here's what I changed it to:
> 
> It was recently discovered that the linux version of waitid is not a
> superset of the other wait functions because it does not include
> support for waiting for the current process group. This has two
> downsides:
> 1. An extra system call is needed to get the current process group.
> 2. After the current process group is received and before it is passed
>    to waitid a signal could arrive causing the current process group to change.

I don't think "downsides" sufficiently conveys that this is hard
breakage of a requirement for waitpid. How about something like the
following?

"It was recently discovered that the linux version of waitid is not a
superset of the other wait functions because it does not include
support for waiting for the current process group. Userspace cannot
simply emulate this functionality with an additional getpgid syscall
due to inherent race conditions that violate the async-signal safety
requirements for waitpid."

Rich

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAKmqyKMJPQAOKn11xepzAwXOd4e9dU0Cyz=A0T-uMEgUp5yJjA@mail.gmail.com>
2019-08-14 11:38 ` [PATCH v1 0/1] waitid: process group enhancement christian.brauner
2019-08-14 11:38   ` [PATCH v1 1/1] waitid: Add support for waiting for the current process group christian.brauner
2019-08-14 12:29     ` Oleg Nesterov
2019-08-14 12:45       ` Christian Brauner
2019-08-14 12:50         ` Oleg Nesterov
2019-08-14 12:53           ` Christian Brauner
2019-08-14 13:07 ` [PATCH v2 0/1] waitid: process group enhancement Christian Brauner
2019-08-14 13:07   ` [PATCH v2 1/1] waitid: Add support for waiting for the current process group Christian Brauner
2019-08-14 14:19     ` Oleg Nesterov
2019-08-14 14:35       ` Christian Brauner
2019-08-14 15:27         ` Oleg Nesterov
2019-08-14 15:30           ` Christian Brauner
2019-08-14 15:43 ` [PATCH v3 0/1] waitid: process group enhancement Christian Brauner
2019-08-14 15:44   ` [PATCH v3 1/1] waitid: Add support for waiting for the current process group Christian Brauner
2019-08-14 16:09     ` Oleg Nesterov
2019-08-14 16:15       ` Christian Brauner
2019-08-14 16:34         ` Christian Brauner
2019-08-14 16:55           ` Rich Felker [this message]
2019-08-14 17:02             ` Christian Brauner
2019-08-14 17:06             ` Linus Torvalds
2019-08-14 18:00               ` Rich Felker
2019-08-14 20:50       ` Christian Brauner
2019-08-14 15:58   ` [PATCH v3 0/1] waitid: process group enhancement Rich Felker
2019-08-14 16:13     ` Christian Brauner

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