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SubjectRe: [PATCH v2 2/5] sched,ptrace: Fix ptrace_check_attach() vs PREEMPT_RT
Oleg Nesterov <oleg@redhat.com> writes:

> On 04/21, Peter Zijlstra wrote:
>>
>> @@ -1329,8 +1337,7 @@ SYSCALL_DEFINE4(ptrace, long, request, l
>> goto out_put_task_struct;
>>
>> ret = arch_ptrace(child, request, addr, data);
>> - if (ret || request != PTRACE_DETACH)
>> - ptrace_unfreeze_traced(child);
>> + ptrace_unfreeze_traced(child);
>
> Forgot to mention... whatever we do this doesn't look right.
>
> ptrace_unfreeze_traced() must not be called if the tracee was untraced,
> anothet debugger can come after that. I agree, the current code looks
> a bit confusing, perhaps it makes sense to re-write it:
>
> if (request == PTRACE_DETACH && ret == 0)
> ; /* nothing to do, no longer traced by us */
> else
> ptrace_unfreeze_traced(child);

This was a bug in my original JOBCTL_DELAY_WAITKILL patch and it was
just cut and pasted here. I thought it made sense when I was throwing
things together but when I looked more closely I realized that it is
not safe.

Eric

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