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Re: [PATCH] [BZ #15392] Remove fork child pid assertion
- From: Ricky Zhou <rickyz at google dot com>
- To: Torvald Riegel <triegel at redhat dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Mon, 17 Nov 2014 14:20:49 -0800
- Subject: Re: [PATCH] [BZ #15392] Remove fork child pid assertion
- Authentication-results: sourceware.org; auth=none
- References: <1416014955-5408-1-git-send-email-rickyz at chromium dot org> <1416220691 dot 4535 dot 385 dot camel at triegel dot csb>
On Mon, Nov 17, 2014 at 2:38 AM, Torvald Riegel <email@example.com> wrote:
> On Fri, 2014-11-14 at 17:29 -0800, Ricky Zhou wrote:
>> This assertion is no longer always true, since a forked child may be in
>> a different PID namespace than its parent, and the two namespace may
>> have PID collisions.
> If that's true, process-shared synchronization facilities based on the
> thread ID (e.g., mutexes) might not work anymore.
> Do we at least need a note in the documentation that this is the case?
> Or do we still need to implement it?
> Is there any glibc-internal synchronization that this could break?
> I believe we deal with these issues before dropping the assert.
Within a PID namespace, all thread IDs should remain unique, and a
process cannot have threads in different PID namespaces
(http://lxr.free-electrons.com/source/kernel/fork.c#L1217), so I'm
having trouble coming up with a situation where removing this assert
would allow badness to happen down the line.