Messages in this thread | | | Subject | Re: ptrace(PTRACE_ATTACH) [no intervering wait] ptrace(PTRACE_DETACH) may leave tracee stuck | From | Mike Galbraith <> | Date | Wed, 24 Jul 2013 04:21:29 +0200 |
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On Tue, 2013-07-23 at 17:58 +0200, Oleg Nesterov wrote: > 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.
Thanks for confirmation. The man page was pretty clear (read it after slogging through source/traces, oh well, educational;) that -ESRCH was expected, but I wanted to be sure about tracee state thereafter.
-Mike
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