Messages in this thread | | | Date | Sun, 23 Nov 2003 09:59:47 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: x86: SIGTRAP handling differences from 2.4 to 2.6 |
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On 22 Nov 2003, H. Peter Anvin wrote: > > > > Hmm.. Looking at the signal sending code, we actually do special-case > > "init" there already - but only for the "kill -1" case. If the test for > > "pid > 1" was moved into "group_send_sig_info()" instead, that would > > pretty much do it, I think. > > > > Okay... I'm going to ask the obvious dumb question: > > Why do we bother special-casing init at all?
Because the kernel depends on it existing. "init" literally _is_ special from a kernel standpoint, because its' the "reaper of zombies" (and, may I add, that would be a great name for a rock band).
So without init, the kernel wouldn't have anybody to fall back on when a parent process dies, and would become very very unhappy. Historically it actually oopsed the kernel.
UNIX semantics literally _require_ that "getppid()" should return 1 if your parent dies, and that's "current->p_parent->tgid". So we have to have a parent with pid 1, and thus init really _is_ special.
Yeah, we could have _other_ special cases (we could create another process that is invisible and has pid 1), but the fact is, _some_ special case is required. It might as well be "you can't kill init".
Linus
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