Re: [PATCH] [BZ #15392] Remove fork child pid assertion

[Torvald Riegel <triegel at redhat dot com>]

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.

> An example program which hits this assert is attached to bug 17596.
> 
> 	[BZ #15392]
> 	* sysdeps/nptl/fork.c (__libc_fork): Remove assert that the parent
> 	and child pid must differ after forking.
> ---
>  sysdeps/nptl/fork.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/sysdeps/nptl/fork.c b/sysdeps/nptl/fork.c
> index a7dafa8..6adb723 100644
> --- a/sysdeps/nptl/fork.c
> +++ b/sysdeps/nptl/fork.c
> @@ -139,8 +139,6 @@ __libc_fork (void)
>      {
>        struct pthread *self = THREAD_SELF;
>  
> -      assert (THREAD_GETMEM (self, tid) != ppid);
> -
>        /* See __pthread_once.  */
>        if (__fork_generation_pointer != NULL)
>  	*__fork_generation_pointer += __PTHREAD_ONCE_FORK_GEN_INCR;