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SubjectRe: [PATCH] Make PTRACE_SEIZE set ptrace options specified in data parameter
On 09/07, Denys Vlasenko wrote:
>
> Make PTRACE_SEIZE set ptrace options specified in data parameter

Personally I think this makes sense, and in fact I suggested this
from the very beginning.

Oh. But since we are goin to establish the API rules, this should
be discussed.

IIRC, Tejun disliked this idea. Tejun?

> retval = -EIO;
> - if (seize && !(flags & PTRACE_SEIZE_DEVEL))
> - goto out;
> + if (seize) {
> + if ((flags & ~(long)PTRACE_O_MASK) != PTRACE_SEIZE_DEVEL)
> + goto out;
> + flags &= ~PTRACE_SEIZE_DEVEL;
> + } else
> + flags = 0;

Personally I do not care, but this is against the coding-style rules. This
should be

} else {
flags = 0;
}
Or, better,

flags = 0;
if (seize) {
flags = ...
}

> @@ -263,7 +267,7 @@ static int ptrace_attach(struct task_struct *task, long request,
> if (task->ptrace)
> goto unlock_tasklist;
>
> - task->ptrace = PT_PTRACED;
> + task->ptrace = PT_PTRACED | (flags << PT_OPT_FLAG_SHIFT);
> if (seize)
> task->ptrace |= PT_SEIZED;

Hmm. Tejun, Denys, this doesn't look exactly right.

I already thought about this before, but somehow I convinced myself
this is fine.

I think we should set both PT_PTRACED | PT_SEIZED "atomically", at
once. Otherwise, say, the tracee can do do_jobctl_trap() in between,
no? Nothing really bad can happen, but we shouldn't lose EVENT_STOP
code.
IOW, I think we need the small fix before this patch.

Oleg.



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