[PATCH] s390: set TIF_RESTARTBLOCK after sys_restart()

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

(this is on top of the patch
	's390: actually restart syscalls after sys_restart'
which I sent last Thursday)

We use TIF_RESTARTBLOCK in do_signal() to tell sys_checkpoint()
to mark the thread as needing a sysc_do_restart to restart an
interrupted syscall after sys_restart().

However, as Oren pointed out, if the task receives a signal
after sys_restart() but before returning to userspace, and
enters do_signal, then conditions will not be met to set
TIF_RESTARTBLOCK.  So if the restarted task freezes here and is
checkpointed, then the resulting checkpoint image will not restart
the interrupted syscall.

So, set TIF_RESTARTBLOCK in sys_restart() if TIF_RESTARTBLOCK was set
at checkpoint.  Clear TIF_RESTARTBLOCK in ssyc_do_restart, so that
if we do not go to do_signal right after sys_restart() we don't
mistakenly keep running with that flag.

To test this, add a dummy handler for SIGUSR1 to cr_tests/sleep/sleeptest.c,
open two terminals, and do:

Terminal 1:                             Terminal :
mount -t cgroup -o freezer freezer /cgroup
mkdir /cgroup/1 /cgroup/2
echo $$ > /cgroup/1/tasks
./sleeptest

                                        echo FROZEN > /cgroup/1/freezer.state
                                        checkpoint `pidof sleeptest` > /tmp/out
                                        thaw

restart -F /cgroup/2 < /tmp/out

                                        kill -USR1 `pidof sleeptest`;
                                        echo THAWED > /cgroup/2/freezer.state ;
                                        sleep 0.3;
                                        echo FROZEN > /cgroup/2/freezer.state;
                                        checkpoint `pidof sleeptest` > /tmp/out2;
                                        echo THAWED > /cgroup/2/freezer.state

restart < /tmp/out2

Without this patch, the final restart will immediately exit.  With
this patch, it will restart the sleep.

Signed-off-by: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 arch/s390/kernel/entry64.S |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index 9aff1d4..798ea9c 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -58,6 +58,7 @@ _TIF_WORK_INT = (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED | \
 		 _TIF_MCCK_PENDING)
 _TIF_SYSCALL = (_TIF_SYSCALL_TRACE>>8 | _TIF_SYSCALL_AUDIT>>8 | \
 		_TIF_SECCOMP>>8 | _TIF_SYSCALL_TRACEPOINT>>8)
+CLR_TIF_RESTARTBLOCK = (255 - (_TIF_RESTARTBLOCK>>16))
 
 #define BASED(name) name-system_call(%r13)
 
@@ -338,6 +339,7 @@ sysc_mcck_pending:
 #
 sysc_sigpending:
 	ni	__TI_flags+7(%r9),255-_TIF_SINGLE_STEP # clear TIF_SINGLE_STEP
+	ni	__TI_flags+6(%r9),CLR_TIF_RESTARTBLOCK # clear TIF_RESTARTBLOCK
 	la	%r2,SP_PTREGS(%r15)	# load pt_regs
 	brasl	%r14,do_signal		# call do_signal
 	tm	__TI_flags+7(%r9),_TIF_RESTART_SVC
-- 
1.6.1