Re: [PATCH] exit: Clarify choice of new parent in forget_original_parent()
From: Kirill Tkhai
Date: Wed Jun 17 2015 - 13:24:42 EST
Ð ÐÑ, 16/06/2015 Ð 22:03 +0200, Oleg Nesterov ÐÐÑÐÑ:
> forgot to mention,
> On 06/16, Oleg Nesterov wrote:
> > On 06/16, Kirill Tkhai wrote:
> > >
> > > + * child_reaper doesn't have children after zap_pid_ns_processes(),
> > > + * therefore it can't enter this function.
> > > + */
> > > + BUG_ON(child_reaper == father);
> > Yes, we can add this BUG_ON(). But please see the comments in
> > zap_pid_ns_processes(). We can change zap_pid_ns_processes() so that
> > it returns with non-empty ->children list due to EXIT_DEAD children.
> > Unlikely we will actually do this, at least soon, so I won't argue
> > with this BUG_ON().
> > But. In this case it would be better to add it into forget_original_parent(),
> > reaper = find_new_reaper(...);
> > BUG_ON(reaper == father);
> because this way:
> 1. This BUG_ON() will still be valid even if we actually change
> zap_pid_ns_processes() to return with EXIT_DEAD children
> 2. If we really want this sanity check, we should not tie it to
> ->child_reaper case.
> OTOH. If for some reason you want to check ->child_reaper only, then
> you should probably do this right after list_empty(&father->children)
> check, or at least before find_alive_thread(). Because otherwise it
> looks confusing, it looks as if "child_reaper == father" is only wrong
> if find_alive_thread(father) fails.
Sure, it's more logical. Thanks, Oleg.
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