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Re: race condition in libports

From: Samuel Thibault
Subject: Re: race condition in libports
Date: Sat, 6 Jan 2018 02:03:11 +0100
User-agent: NeoMutt/20170113 (1.7.2)


Brent W. Baccala, on ven. 05 janv. 2018 19:47:37 -0500, wrote:
> Well, in that case, perhaps it should work by checking to see if the port is 
> in
> the hash, rather than by looking at how many weak references it's got. 
> Something more like this:
>   if ((refcounts_hard_references(&i->pi.refcounts) == 0)
>       && (* i->id_hashloc == i))
>     {
>       /* Nobody got a send right in between, we can remove from the hash.  */
>       hurd_ihash_locp_remove (&idhash, i->id_hashloc);
>       ports_port_deref_weak (&i->pi);
>     }

You can't afford dereferencing id_hashloc like that: it could have
gotten away in between.

Could you try the attached patch instead?

> Also, what documentation?  The hurd texinfo file?  That's the only place that 
> I
> know of where this is documented.

Yes: “If nonzero, @var{dropweak_routine} will be called to request
weak references to be dropped.” It doesn't say "one weak reference", but
"weak references".


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