linux-kernel - Re: [PATCH v3 1/1] waitid: Add support for waiting for the current process group

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Message-ID: <20190814163443.6odsksff4jbta7be@wittgenstein>
Date:   Wed, 14 Aug 2019 18:34:44 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     linux-kernel@...r.kernel.org, libc-alpha@...rceware.org,
        alistair23@...il.com, ebiederm@...ssion.com, arnd@...db.de,
        dalias@...c.org, torvalds@...ux-foundation.org,
        adhemerval.zanella@...aro.org, fweimer@...hat.com,
        palmer@...ive.com, macro@....com, zongbox@...il.com,
        akpm@...ux-foundation.org, viro@...iv.linux.org.uk, hpa@...or.com
Subject: Re: [PATCH v3 1/1] waitid: Add support for waiting for the current
 process group

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.

Christian