Messages in this thread | | | Date | Sun, 15 May 2011 18:10:00 +0200 | From | Jan Kratochvil <> | Subject | PTRACE_DETACH without stop [Re: [PATCH 04/11] ptrace: implement PTRACE_INTERRUPT] |
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On Wed, 11 May 2011 11:19:55 +0200, Tejun Heo wrote: > On Tue, May 10, 2011 at 11:59:58PM +0200, Denys Vlasenko wrote: > > Another note: even though PTRACE_INTERRUPT solves the problem that > > PTRACE_DETACH of a running tracee was butt-ugly thing to do correctly, > > the "new" way is still a bit ugly: tracer needs PTRACE_INTERRUPT, > > waitpid, and only then PTRACE_DETACH. Why not go all the way > > and make PTRACE_DETACH work on running tracee too? > > I don't think I'll change that. It's only three syscall sequence - > INTERRUPT, wait(STOPPED) and DETACH which will always work reliably > (unless tracee gets killed or something).
I do not think this change is much related to this patchset.
But having to PTRACE_INTERRUPT the tracee before PTRACE_DETACH has no advantage, it is just a performance (see transparent tracking of 10000+ thread https://lkml.org/lkml/2011/5/15/115 ) problem and also getting it correct. As when one wait()s and gets WIFSTOPPED one needs to respawn to signal otherwise the signal gets lost on PTRACE_ATTACH. How to respawn it? By PTRACE_INTERRUPT with DATA==signal? Or PTRACE_CONT with DATA==signal? With rapid signalling of the tracee the debugger may never have a chance to correctly quit. Handling other cases transparently for the original parent also may not be fully clear.
It would be nice to write documentation already while discussing this patch, I do not know if PTRACE_INTERRUPT respects DATA etc., it may show ptrace is still tricky.
Thanks, Jan
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