[PATCH RFC] checkpoint: handle saved_sigmask

[Serge E. Hallyn]

Each arch seems to have its own way of specifying that
current->saved_sigmask should contains the valid blocked
sigmask.  So provide an arch-specific hook for that test,
and, if true, then store saved_sigmask in place of blocked
in the checkpoint image.  None of the architectures currently
save these flags, so we don't need to do anything special
to unset them after restart.

If right after sys_restart the a signal needs to be handled
(which was sent during restart) then it will just do the right
thing (save blocked back to saved_sigmask and set
TIF_RESTORE_SIGMASK or whatever).

Thoughts?

Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>
---
 arch/powerpc/kernel/signal.c  |    9 +++++++++
 arch/s390/kernel/checkpoint.c |    2 --
 arch/s390/kernel/signal.c     |    7 +++++++
 arch/x86/kernel/signal.c      |    6 ++++++
 checkpoint/signal.c           |    5 ++++-
 include/linux/signal.h        |    6 ++++++
 6 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index 00b5078..4aa0128 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -188,6 +188,15 @@ static int do_signal_pending(sigset_t *oldset, struct pt_regs *regs)
 	return ret;
 }
 
+int task_restore_sigmask(struct task_struct *task)
+{
+	struct thread_info *ti = task_thread_info(task);
+	if (ti->local_flags & _TLF_RESTORE_SIGMASK)
+		return 1;
+	return 0;
+}
+
+
 void do_signal(struct pt_regs *regs, unsigned long thread_info_flags)
 {
 	if (thread_info_flags & _TIF_SIGPENDING)
diff --git a/arch/s390/kernel/checkpoint.c b/arch/s390/kernel/checkpoint.c
index 092fd87..048e820 100644
--- a/arch/s390/kernel/checkpoint.c
+++ b/arch/s390/kernel/checkpoint.c
@@ -200,8 +200,6 @@ int restore_thread(struct ckpt_ctx *ctx)
 		set_thread_flag(TIF_RESTARTBLOCK);
 	}
 
-	/* need to do something with TIF_RESTORE_SIGMASK ? */
-
 	ckpt_hdr_put(ctx, h);
 	return 0;
 }
diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
index 503fd09..0654f12 100644
--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -538,6 +538,13 @@ void do_signal(struct pt_regs *regs)
 	}
 }
 
+int task_restore_sigmask(struct task_struct *task)
+{
+	if (test_tsk_thread_flag(task, TIF_RESTORE_SIGMASK))
+		return 1;
+	return 0;
+}
+
 void do_notify_resume(struct pt_regs *regs)
 {
 	clear_thread_flag(TIF_NOTIFY_RESUME);
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 6a44a76..a6e8035 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -849,6 +849,12 @@ static void do_signal(struct pt_regs *regs)
 	}
 }
 
+int task_restore_sigmask(struct task_struct *task) {
+	if (task_thread_info(t)->status & TS_RESTORE_SIGMASK)
+		return 1;
+	return 0;
+}
+
 /*
  * notification of userspace execution resumption
  * - triggered by the TIF_WORK_MASK flags
diff --git a/checkpoint/signal.c b/checkpoint/signal.c
index 609e924..ad95e0c 100644
--- a/checkpoint/signal.c
+++ b/checkpoint/signal.c
@@ -682,7 +682,10 @@ int checkpoint_task_signal(struct ckpt_ctx *ctx, struct task_struct *t)
 	if (!h)
 		return -ENOMEM;
 
-	fill_sigset(&h->blocked, &t->blocked);
+	if (task_restore_sigmask(t))
+		fill_sigset(&h->blocked, &t->saved_sigmask);
+	else
+		fill_sigset(&h->blocked, &t->blocked);
 
 	ret = ckpt_write_obj(ctx, &h->h);
 	ckpt_hdr_put(ctx, h);
diff --git a/include/linux/signal.h b/include/linux/signal.h
index ab9272c..aa18432 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -376,6 +376,12 @@ int unhandled_signal(struct task_struct *tsk, int sig);
 
 void signals_init(void);
 
+/*
+ * arch-specific query, used at checkpoint: should saved_sigmask be used
+ * in place of blocked
+ */
+int task_restore_sigmask(struct task_struct *task);
+
 #endif /* __KERNEL__ */
 
 #endif /* _LINUX_SIGNAL_H */
-- 
1.6.1