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Re: [PATCH v2 3/3] posix: New Linux posix_spawn{p} implementation
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: Torvald Riegel <triegel at redhat dot com>
- Cc: Florian Weimer <fweimer at redhat dot com>, libc-alpha at sourceware dot org
- Date: Wed, 3 Feb 2016 10:05:03 -0200
- Subject: Re: [PATCH v2 3/3] posix: New Linux posix_spawn{p} implementation
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- References: <1454343665-1706-1-git-send-email-adhemerval dot zanella at linaro dot org> <1454343665-1706-4-git-send-email-adhemerval dot zanella at linaro dot org> <56B0A9B7 dot 6000507 at redhat dot com> <56B0AFBB dot 4050402 at linaro dot org> <1454497614 dot 4592 dot 392 dot camel at localhost dot localdomain>
On 03-02-2016 09:06, Torvald Riegel wrote:
> On Tue, 2016-02-02 at 11:31 -0200, Adhemerval Zanella wrote:
>>
>> On 02-02-2016 11:05, Florian Weimer wrote:
>>> On 02/01/2016 05:21 PM, Adhemerval Zanella wrote:
>>>
>>>> + new_pid = CLONE (__spawni_child, STACK (stack, stack_size),
>>>> + CLONE_VM | CLONE_VFORK | SIGCHLD, &args);
>>>
>>> Does this set up new per-thread variables? Otherwise, errno in the
>>> parent and child will be same and the code still has races.
>>>
>>> Florian
>>>
>>
>> Could you elaborate? In my understanding there is no requirement of
>> using CLONE_SETTLS to avoid races: CLONE_VFORK will suspend the
>> calling process and even with child using the same TLS namespace as
>> the parent there will be no concurrent access between them.
>
> Whatever you agree on eventually, it sounds as if this should be
> documented as part of the concurrency notes for this function.
>
I think it is worth to comment internally on the function implementation
about the CLONE_VFORK synchronization, but since it is transparent
to user (the function will either spawn a new process or fails and it can
be either through a syscall, {v}fork/exec or any other mechanism),
I do not see why expose these implementation details explicit.