proc: always store parent pid in p_oppid

[mjg]

Summary

Doing so removes the dependency on proctree lock from sysctl process list export which further reduces contention during poudriere -j 128 runs.

While here adjust getppid.

Test Plan

kyua, poudriere

[kib]

The patch seems to be generated on top of D17817 and is not applicable.

I do not like proc_reparent_ptrace() addition, just expand the signature of proc_reparent() with the new arg.

sys/kern/kern_exit.c

115

Now that the condition is simplified, it can be written as

return (child->p_pptr->p_pid == child->p_oppid ? child->p_pptr : initproc);

sys/kern/kern_prot.c

126–127

ppid is not needed. Just

return (p->p_oppid);

is enough.

sys/sys/proc.h

598

The comment needs updating, it no longer has anything to do with ptrace.

[mjg]

• address feedback
• regen against head
• i did not change the condition in proc_realparent as it goes way over the 80 char limit

[kib]

sys/kern/kern_exit.c

111

I think it really useful to add MPASS(child->p_oppid != 0) asserts at all places where old chode checked for p_oppid == 0.

115

The line would just wrap, I still think that saving three lines is good.

117

Can this list walk replaced by lookup by p_oppid ?

[mjg]

sys/kern/kern_exit.c

111

we can't easily assert here. the original condition has ||. I don't think it adds much to the other place.

115

well i can put this if you insist:

+       if ((child->p_treeflag & P_TREE_ORPHANED) == 0)
+               return (child->p_pptr->p_pid == child->p_oppid ?
+                           child->p_pptr : initproc);

I'm temporarily on a very slow connection and can't upload the 300KB+ diff arc requires without timing out

117

it would require adding allproc here. (or the relevant hash lock after they get added later). i think this is a consideration unrelated to the patch.

[kib]

sys/kern/kern_exit.c

111

I do not understand why. It should be non-conditional case now.

115

Assuming the continuation line uses +4 spaces, this looks fine.