On 07/23, Mike Galbraith wrote: > > I received a report that glibc:elf/pldd hangs occasionally, and indeed.. > > for i in `seq 1 1000`; do taskset -c 3 pldd $$ > /dev/null 2>&1; done > > ..will do so. Rummage..... > > ptrace(PTRACE_DETACH) returns -ESRCH when the trap hasn't happened yet, > which happens because pldd doesn't wait() before ptrace(PTRACE_DETACH). > > pldd source: > [...snip...] > > Seems this usually works only because cycles expended between attach and > detach is usually enough to let trap happen so tracee can set its state > to TASK_TRACED as PTRACE_DETACH expects it to be. > > Is this expected behavior?
Yes. PTRACE_ATTACH + PTRACE_DETACH is not correct without wait() in between, this is expected. PTRACE_DETACH like (almost) any other ptrace request needs the stopped tracee. Otherwise, say, ptrace_disable() or flush_ptrace_hw_breakpoint() are not safe. We could probably add PTRACE_UNTRACE which only does __ptrace_unlink/etc like the exiting tracer does. (In particular, it could help to detach a zombie). But note that even PTRACE_ATTACH + PTRACE_UNTRACE won't be really correct. PTRACE_ATTACH sends SIGSTOP, so without sys_wait() in between the tracee can stop in TASK_STOPPED. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
