From 8a88951b5878dc475dcd841cefc767e36397d14e Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 4 Jan 2012 17:29:20 +0100 Subject: [PATCH] ptrace: ensure JOBCTL_STOP_SIGMASK is not zero after detach This is the temporary simple fix for 3.2, we need more changes in this area. 1. do_signal_stop() assumes that the running untraced thread in the stopped thread group is not possible. This was our goal but it is not yet achieved: a stopped-but-resumed tracee can clone the running thread which can initiate another group-stop. Remove WARN_ON_ONCE(!current->ptrace). 2. A new thread always starts with ->jobctl = 0. If it is auto-attached and this group is stopped, __ptrace_unlink() sets JOBCTL_STOP_PENDING but JOBCTL_STOP_SIGMASK part is zero, this triggers WANR_ON(!signr) in do_jobctl_trap() if another debugger attaches. Change __ptrace_unlink() to set the artificial SIGSTOP for report. Alternatively we could change ptrace_init_task() to copy signr from current, but this means we can copy it for no reason and hide the possible similar problems. Acked-by: Tejun Heo Cc: [3.1] Signed-off-by: Oleg Nesterov Signed-off-by: Linus Torvalds --- kernel/ptrace.c | 13 ++++++++++++- kernel/signal.c | 2 -- 2 files changed, 12 insertions(+), 3 deletions(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 24d04477b257..78ab24a7b0e4 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -96,9 +96,20 @@ void __ptrace_unlink(struct task_struct *child) */ if (!(child->flags & PF_EXITING) && (child->signal->flags & SIGNAL_STOP_STOPPED || - child->signal->group_stop_count)) + child->signal->group_stop_count)) { child->jobctl |= JOBCTL_STOP_PENDING; + /* + * This is only possible if this thread was cloned by the + * traced task running in the stopped group, set the signal + * for the future reports. + * FIXME: we should change ptrace_init_task() to handle this + * case. + */ + if (!(child->jobctl & JOBCTL_STOP_SIGMASK)) + child->jobctl |= SIGSTOP; + } + /* * If transition to TASK_STOPPED is pending or in TASK_TRACED, kick * @child in the butt. Note that @resume should be used iff @child diff --git a/kernel/signal.c b/kernel/signal.c index b3f78d09a105..206551563cce 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1994,8 +1994,6 @@ static bool do_signal_stop(int signr) */ if (!(sig->flags & SIGNAL_STOP_STOPPED)) sig->group_exit_code = signr; - else - WARN_ON_ONCE(!current->ptrace); sig->group_stop_count = 0; -- 2.20.1