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Date: Wed, 24 Jul 2013 04:21:29 +0200 From: Mike Galbraith <bitbucket@...ine.de> To: Oleg Nesterov <oleg@...hat.com> Cc: LKML <linux-kernel@...r.kernel.org> Subject: Re: ptrace(PTRACE_ATTACH) [no intervering wait] ptrace(PTRACE_DETACH) may leave tracee stuck 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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