[PATCH] ptrace: add ability to get/set signal-blocked mask (v2)

[PATCH] ptrace: add ability to get/set signal-blocked mask (v2)

[Andrey Vagin]

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.

I think gdb can use this commands too.

v2: Don't use __set_task_blocked with tsk != current.
recalc_sigpending() is not called here, because it will be called after
resume. retarget_shared_pending() are not called, because we suppose,
that other threads are stopped too.

Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
 include/uapi/linux/ptrace.h |  3 +++
 kernel/ptrace.c             | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index 52ebcc8..cf1019e 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -61,6 +61,9 @@ struct ptrace_peeksiginfo_args {
 	__s32 nr;	/* how may siginfos to take */
 };
 
+#define PTRACE_GETSIGMASK	0x420a
+#define PTRACE_SETSIGMASK	0x420b
+
 /* Read signals from a shared (process wide) queue */
 #define PTRACE_PEEKSIGINFO_SHARED	(1 << 0)
 
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 17ae54d..bebe67e 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -841,6 +841,48 @@ 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;
+		else
+			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));
+
+		/*
+		 * Every thread does recalc_sigpending() after resume, so
+		 * retarget_shared_pending() and recalc_sigpending() are not
+		 * called here.
+		 */
+		spin_lock_irq(&child->sighand->siglock);
+		child->blocked = new_set;
+		spin_unlock_irq(&child->sighand->siglock);
+
+		ret = 0;
+		break;
+	}
+
 	case PTRACE_INTERRUPT:
 		/*
 		 * Stop tracee without any side-effect on signal or job
-- 
1.8.1.4

Re: [PATCH] ptrace: add ability to get/set signal-blocked mask (v2)

[Oleg Nesterov]

On 04/23, Andrey Vagin wrote:
>
> @@ -841,6 +841,48 @@ 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;

Yes, we can do this lockless. Only the task itself (or the debugger with
this patch) can change ->blocked, and the tracee can't run.

> +	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));
> +
> +		/*
> +		 * Every thread does recalc_sigpending() after resume, so
> +		 * retarget_shared_pending() and recalc_sigpending() are not
> +		 * called here.
> +		 */
> +		spin_lock_irq(&child->sighand->siglock);
> +		child->blocked = new_set;
> +		spin_unlock_irq(&child->sighand->siglock);
> +
> +		ret = 0;
> +		break;
> +	}

And this looks fine too.

Personally I am not sure we need to check addr == sizeof(), debugger
should know what it does... But I won't argue.

Oleg.

Re: [PATCH] ptrace: add ability to get/set signal-blocked mask (v2)

[Andrew Vagin]

Andrew, let me know if you are waiting something to accept this patch.

Thanks.

On Tue, Apr 23, 2013 at 05:21:43PM +0200, Oleg Nesterov wrote:
> On 04/23, Andrey Vagin wrote:
> >
> > @@ -841,6 +841,48 @@ 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;
> 
> Yes, we can do this lockless. Only the task itself (or the debugger with
> this patch) can change ->blocked, and the tracee can't run.
> 
> > +	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));
> > +
> > +		/*
> > +		 * Every thread does recalc_sigpending() after resume, so
> > +		 * retarget_shared_pending() and recalc_sigpending() are not
> > +		 * called here.
> > +		 */
> > +		spin_lock_irq(&child->sighand->siglock);
> > +		child->blocked = new_set;
> > +		spin_unlock_irq(&child->sighand->siglock);
> > +
> > +		ret = 0;
> > +		break;
> > +	}
> 
> And this looks fine too.
> 
> Personally I am not sure we need to check addr == sizeof(), debugger
> should know what it does... But I won't argue.

We do the same thing in sys_rt_sigaction. I think it may be useful in a
future, if we decide to change the size of sigset_t.

> 
> Oleg.
> 

[PATCH] ptrace: add ability to get/set signal-blocked mask (v2)

[Andrey Vagin]

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.

I think gdb can use this commands too.

v2: Don't use __set_task_blocked with tsk != current.
recalc_sigpending() is not called here, because it will be called after
resume. retarget_shared_pending() are not called, because we suppose,
that other threads are stopped too.

Cc: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
 include/uapi/linux/ptrace.h |  3 +++
 kernel/ptrace.c             | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index 52ebcc8..cf1019e 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -61,6 +61,9 @@ struct ptrace_peeksiginfo_args {
 	__s32 nr;	/* how may siginfos to take */
 };
 
+#define PTRACE_GETSIGMASK	0x420a
+#define PTRACE_SETSIGMASK	0x420b
+
 /* Read signals from a shared (process wide) queue */
 #define PTRACE_PEEKSIGINFO_SHARED	(1 << 0)
 
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index aed981a..f7f6112 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -842,6 +842,48 @@ 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;
+		else
+			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));
+
+		/*
+		 * Every thread does recalc_sigpending() after resume, so
+		 * retarget_shared_pending() and recalc_sigpending() are not
+		 * called here.
+		 */
+		spin_lock_irq(&child->sighand->siglock);
+		child->blocked = new_set;
+		spin_unlock_irq(&child->sighand->siglock);
+
+		ret = 0;
+		break;
+	}
+
 	case PTRACE_INTERRUPT:
 		/*
 		 * Stop tracee without any side-effect on signal or job
-- 
1.8.1.4