linux-kernel - Re: [PATCH 1/1] proc: make /proc/self point to thread

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Message-ID: <CA+55aFwwLtxWbNnHO-8Nrpo5q9W=3D-oubUeJ3pFZCxCa4__RQ@mail.gmail.com>
Date:	Tue, 27 Aug 2013 11:15:56 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Willy Tarreau <w@....eu>, Al Viro <viro@...iv.linux.org.uk>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Brad Spengler <spender@...ecurity.net>
Subject: Re: [PATCH 1/1] proc: make /proc/self point to thread

On Tue, Aug 27, 2013 at 10:49 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> Why? To me /proc/self == /proc/$((sys_gettid)) looks more natural.
> Say, /proc/self/task... But this is subjective.

Actually, you're right - I incorrectly thought we had removed the
thread id lookup from the top level in /proc. But we never actually
did that. We only removed them from readdir.

So while you won't see thread id's in the directory listing, we *do*
successfully look up thread id's when specified explicitly. It's
confusing, but it happens to work. So you can do

   ls -l /proc/<tid>/

and get the expected result, but if you do

   ls -l /proc | grep <tid>

it won't actually show up unless the thread ID is also the thread group leader.

> Although to be honest, I was seduced by "Worth testing". I mean I am
> just curious, who can suffer from this change? Nevermind, please
> ignore.

Yeah, if we were to redesign /proc I'd do it differently, but I think
we should just accept that it works "well enough" and there's just too
much risk from making changes that aren't strictly required.

            Linus
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