Re: [PATCH v2 1/2] util/log: Derive thread id from getpid() on hosts w/o gettid() syscall

[Greg Kurz <groug@kaod.org>]

On Thu, 20 Oct 2022 12:39:41 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 10/19/22 17:57, Daniel P. Berrangé wrote:
> >> +    if (my_id == -1) {
> >> +        my_id = getpid() + qatomic_fetch_inc(&counter);
> >> +    }
> >> +    return my_id;
> > This doesn't look safe for linux-user when we fork, but don't exec.
> 
> Linux-user won't ever get here, however bsd-user might.  We should have 
> get_thread_id() somewhere in util/, for example
> 
> https://github.com/wine-mirror/wine/blob/master/dlls/ntdll/unix/server.c
> 

We have qemu_get_thread_id() already :

https://git.qemu.org/?p=qemu.git;a=blob;f=util/oslib-posix.c;h=827a7aadba444cdb128284f5b4ba43934c78c3db;hb=HEAD#l96

> > The getpid() will change after the fork, but counter won't be
> > reset, so a thread in the parent could clash with a thread
> > in the forked child.
> 
> It might clash even if the counter is reset for that matter.
> 

Yes.

> Paolo
>