[CRIU] [PATCH] ptrace: add ability to get/set signal-blocked mask

[Pavel Emelyanov]

On 04/19/2013 04:58 PM, Andrey Vagin wrote:
> crtools uses a parasite code for dumping processes. The parasite code is
> injected into a process with help PTRACE_SEIZE.
> 
> Currently crtools blocks signals from a parasite code. If a process has
> pending signals, crtools wait while a process handles these signals.
> 
> This method is not suitable for stopped tasks. A stopped task can have a
> few pending signals, when we will try to execute a parasite code, we
> will need to drop SIGSTOP, but all other signals must remain pending,
> because a state of processes must not be changed during checkpointing.
> 
> This patch adds two ptrace commands to set/get signal-blocked mask.

Try to communicate with Oleg and others on this.

> I think gdb can use this commands too.
> 
> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> ---
>  include/linux/signal.h      |  1 +
>  include/uapi/linux/ptrace.h |  2 ++
>  kernel/ptrace.c             | 35 +++++++++++++++++++++++++++++++++++
>  kernel/signal.c             |  2 +-
>  4 files changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/signal.h b/include/linux/signal.h
> index a2dcb94..706b88d 100644
> --- a/include/linux/signal.h
> +++ b/include/linux/signal.h
> @@ -246,6 +246,7 @@ extern int do_sigtimedwait(const sigset_t *, siginfo_t *,
>  extern int sigprocmask(int, sigset_t *, sigset_t *);
>  extern void set_current_blocked(sigset_t *);
>  extern void __set_current_blocked(const sigset_t *);
> +extern void __set_task_blocked(struct task_struct *tsk, const sigset_t *newset);
>  extern int show_unhandled_signals;
>  extern int sigsuspend(sigset_t *);
>  
> diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
> index 52ebcc8..1527684 100644
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -54,6 +54,8 @@
>  #define PTRACE_LISTEN		0x4208
>  
>  #define PTRACE_PEEKSIGINFO	0x4209
> +#define PTRACE_GETSIGMASK	0x420a
> +#define PTRACE_SETSIGMASK	0x420b
>  
>  struct ptrace_peeksiginfo_args {
>  	__u64 off;	/* from which siginfo to start */
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 17ae54d..46415ae 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -841,6 +841,41 @@ int ptrace_request(struct task_struct *child, long request,
>  			ret = ptrace_setsiginfo(child, &siginfo);
>  		break;
>  
> +	case PTRACE_GETSIGMASK:
> +		if (addr != sizeof(sigset_t)) {
> +			ret = -EINVAL;
> +			break;
> +		}
> +
> +		if (copy_to_user(datavp, &child->blocked, sizeof(sigset_t)))
> +			ret = -EFAULT;
> +
> +		ret = 0;
> +		break;
> +
> +	case PTRACE_SETSIGMASK:
> +	{
> +		sigset_t new_set;
> +
> +		if (addr != sizeof(sigset_t)) {
> +			ret = -EINVAL;
> +			break;
> +		}
> +
> +		if (copy_from_user(&new_set, datavp, sizeof(sigset_t))) {
> +			ret = -EFAULT;
> +			break;
> +		}
> +
> +		sigdelsetmask(&new_set, sigmask(SIGKILL)|sigmask(SIGSTOP));
> +
> +		spin_lock_irq(&child->sighand->siglock);
> +		__set_task_blocked(child, &new_set);
> +		spin_unlock_irq(&child->sighand->siglock);
> +
> +		ret = 0;
> +		break;
> +	}
>  	case PTRACE_INTERRUPT:
>  		/*
>  		 * Stop tracee without any side-effect on signal or job
> diff --git a/kernel/signal.c b/kernel/signal.c
> index dd72567..d757e5b 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2522,7 +2522,7 @@ long do_no_restart_syscall(struct restart_block *param)
>  	return -EINTR;
>  }
>  
> -static void __set_task_blocked(struct task_struct *tsk, const sigset_t *newset)
> +void __set_task_blocked(struct task_struct *tsk, const sigset_t *newset)
>  {
>  	if (signal_pending(tsk) && !thread_group_empty(tsk)) {
>  		sigset_t newblocked;
>