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SubjectRe: ptrace warning due to "cgroup: get rid of cgroup_freezer_frozen_exit()"
On 05/07, Roman Gushchin wrote:
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2484,9 +2484,6 @@ bool get_signal(struct ksignal *ksig)
> sigdelset(&current->pending.signal, SIGKILL);
> recalc_sigpending();
> current->jobctl &= ~JOBCTL_TRAP_FREEZE;

just noticed... perhaps it makes more sense to clear JOBCTL_TRAP_FREEZE
before recalc_sigpending(). Or simply not clear it at all, see below.

> - spin_unlock_irq(&sighand->siglock);
> - if (unlikely(cgroup_task_frozen(current)))
> - cgroup_leave_frozen(true);
> goto fatal;
> }
>
> @@ -2608,8 +2605,10 @@ bool get_signal(struct ksignal *ksig)
> continue;
> }
>
> - spin_unlock_irq(&sighand->siglock);
> fatal:
> + spin_unlock_irq(&sighand->siglock);
> + if (unlikely(cgroup_task_frozen(current)))
> + cgroup_leave_frozen(true);

Yes, ptrace_signal() can return a fatal signal... and in this case we do not
clear JOBCTL_TRAP_FREEZE. This doesn't look consistent with the code above.



I can only repeat that somehow we need to cleanup/improve the whole logic.

Say, a traced task reports syscall-enter. ptrace_stop() does enter_frozen().
The cgroup can become CGRP_FROZEN after that. Now the debugger does PTRACE_CONT,
the frozen task actually starts the syscall. Obviously not good.

Heh, and if this syscall is sys_exit or sys_exit_group we can hit the same
warning.

Oleg.

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