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Subject: Re: [patch] threading fix, tid-2.5.47-A3
From: Luca Barbieri <ldb@ldb.ods.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@transmeta.com>,
       Linux-Kernel ML <linux-kernel@vger.kernel.org>,
       Ulrich Drepper <drepper@redhat.com>
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> On 17 Nov 2002, Luca Barbieri wrote:
>=20
> > I don't understand this: why would glibc use it in exec()?
>=20
> i suspect the idea would be to always make every process a proper pthread
> object as well. (but Ulrich will correct me if this is not the case.) Thi=
s
> means that across fork() we can set up the TID pointer via CLONE_SETTID,
> and after exec() we need the new set_tid_address() syscall to initialize
> it.
"after exec()" =3D=3D "in the initialization code for the exec'ed program"?
=20
> if CLONE_VM is set then the TID is set immediately, before sys_clone() =20
> returns. Or are you worried about the fork() case?
Yes.

> this would be fine to me, but i wanted to get away with a single pointer.
Using two pointers would allow to provide all the functionality
mentioned in the discussion on your first clone/tid patch
<http://www.uwsg.iu.edu/hypermail/linux/kernel/0208.1/1409.html>.

Calling sys_set_tid_address after fork is equivalent (but non-atomic)
but requires an additional system call.

> Also, this makes the TID value
> nonatomic - debugging code would have to know whether the child has
> already executed the syscall.
Debugging tools already need to be aware of this for process
initialization, so this shouldn't be a serious problem.


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