(This is a patch against the checkpoint/restart kernel tree at
http://git.ncl.cs.columbia.edu/?p=linux-cr.git;a=shortlog;h=refs/heads/ckpt-v19-rc2.9)
On x86, do_signal() leaves -516 in eax while it freezes, which
sys_restart() can use to detect that it should restart the
syscall which was interrupted by a signal (or the freezer).
On s390, gprs[2] gets tweaked to -EINTR (-4) instead, leaving
us no reliable way to tell whether should be restarted. If the
task is checkpointed here and then restarted, then the last part
of do_signal() won't be done, and the interrupted syscall won't
be restarted.
This patch defines TIF_RESTARTBLOCK as a thread flag showing that
the thread expects to be frozen while kicked out of a restartable
syscall by a signal.
The TIF_RESTARTBLOCK flag is only set for the duration of the
get get_signal_to_deliver() which is where the task may get
frozen. We also set it in sys_restart() if the checkpointed task
had had TIF_RESTARTBLOCK set. It will get cleared if upon exiting
sys_restart() we jump to sysc_sigpending. If instead we jump back
to do_signal(), then TIF_RESTARTBLOCK will stay set again until
after get_signal_to_deliver() so that if it immediately freezes and
is re-checkpointed, the resulting second checkpoint image again
will have TIF_RESTARTBLOCK set.
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 first restart will immediately exit. Without
re-setting TIF_RESTARTBLOCK in sys_restart(), the second restart will
immediately exit. With this full patch, it will restart the sleep
correctly.
Cc: [email protected]
Signed-off-by: Serge E. Hallyn <[email protected]>
---
arch/s390/include/asm/checkpoint_hdr.h | 5 +++
arch/s390/include/asm/thread_info.h | 2 +
arch/s390/kernel/checkpoint.c | 52 +++++++++++++++++++++++++++++++-
arch/s390/kernel/entry64.S | 2 +
arch/s390/kernel/signal.c | 6 ++++
5 files changed, 66 insertions(+), 1 deletions(-)
diff --git a/arch/s390/include/asm/checkpoint_hdr.h
b/arch/s390/include/asm/checkpoint_hdr.h
index a8c2a3d..fd8be2a 100644
--- a/arch/s390/include/asm/checkpoint_hdr.h
+++ b/arch/s390/include/asm/checkpoint_hdr.h
@@ -76,6 +76,11 @@ struct ckpt_hdr_cpu {
__u8 instruction_fetch;
};
+struct ckpt_hdr_thread {
+ struct ckpt_hdr h;
+ __u64 thread_info_flags;
+};
+
struct ckpt_hdr_mm_context {
struct ckpt_hdr h;
unsigned long vdso_base;
diff --git a/arch/s390/include/asm/thread_info.h
b/arch/s390/include/asm/thread_info.h
index 07eb61b..6ef11b2 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -100,6 +100,7 @@ static inline struct thread_info *current_thread_info(void)
#define TIF_MEMDIE 19
#define TIF_RESTORE_SIGMASK 20 /* restore signal mask in do_signal() */
#define TIF_FREEZE 21 /* thread is freezing for suspend */
+#define TIF_RESTARTBLOCK 23 /* use restart block after sys_restart
*/
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
#define _TIF_RESTORE_SIGMASK (1<<TIF_RESTORE_SIGMASK)
@@ -116,6 +117,7 @@ static inline struct thread_info *current_thread_info(void)
#define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG)
#define _TIF_31BIT (1<<TIF_31BIT)
#define _TIF_FREEZE (1<<TIF_FREEZE)
+#define _TIF_RESTARTBLOCK (1<<TIF_RESTARTBLOCK)
#endif /* __KERNEL__ */
diff --git a/arch/s390/kernel/checkpoint.c b/arch/s390/kernel/checkpoint.c
index 60ba04d..092fd87 100644
--- a/arch/s390/kernel/checkpoint.c
+++ b/arch/s390/kernel/checkpoint.c
@@ -65,6 +65,16 @@ static void s390_copy_regs(int op, struct ckpt_hdr_cpu *h,
BUG_ON(h->gprs[2] < 0);
h->gprs[2] = 0;
}
+
+ /*
+ * if checkpoint was taken while interrupted from restartable
+ * system call, then restore_thread() will have already reset
+ * TIF_RESTARTBLOCK, but it did not set gprs[2]. It's easier to
+ * do that here where gprs registers are all restored.
+ */
+ if (op == CKPT_RST && test_thread_flag(TIF_RESTARTBLOCK))
+ regs->gprs[2] = __NR_restart_syscall;
+
CKPT_COPY_ARRAY(op, h->fprs, thr->fp_regs.fprs, NUM_FPRS);
CKPT_COPY_ARRAY(op, h->acrs, thr->acrs, NUM_ACRS);
CKPT_COPY_ARRAY(op, h->per_control_regs,
@@ -83,12 +93,24 @@ static void s390_mm(int op, struct ckpt_hdr_mm_context *h,
int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
{
+ struct ckpt_hdr_thread *h;
+ int ret;
+
/* we will eventually support this, as we do on x86-64 */
if (test_tsk_thread_flag(t, TIF_31BIT)) {
ckpt_err(ctx, -EINVAL, "checkpoint of 31-bit task\n");
return -EINVAL;
}
- return 0;
+
+ h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_THREAD);
+ if (!h)
+ return -ENOMEM;
+
+ h->thread_info_flags = task_thread_info(t)->flags;
+ ret = ckpt_write_obj(ctx, &h->h);
+ ckpt_hdr_put(ctx, h);
+
+ return ret;
}
/* dump the cpu state and registers of a given task */
@@ -148,11 +170,39 @@ int checkpoint_mm_context(struct ckpt_ctx *ctx, struct
mm_struct *mm)
int restore_thread(struct ckpt_ctx *ctx)
{
+ struct ckpt_hdr_thread *h;
+
/* a 31-bit task cannot call sys_restart right now */
if (test_thread_flag(TIF_31BIT)) {
ckpt_err(ctx, -EINVAL, "restart from 31-bit task\n");
return -EINVAL;
}
+
+ h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_THREAD);
+ if (IS_ERR(h))
+ return PTR_ERR(h);
+
+ /*
+ * if the checkpointed task was frozen in a syscall with
+ * -ERESTART_RESTARTBLOCK (switched to -EINTR during do_signal()
+ * before try_to_freeze() happened) then after restart we need
+ * to call __NR_restart_syscall to continue. Fix up here.
+ * In other words, we're doing the rest of the fixup which the
+ * end of do_signal(), which won't now be run, would have done.
+ *
+ * We also re-set TIF_RESTARTBLOCK in case we hit do_signal
+ * right after sys_restart() instead of sysc_restart, since
+ * we would enter do_signal() with different inital conditions
+ * than usual for being "inside" a restartable syscall.
+ */
+ if (h->thread_info_flags & _TIF_RESTARTBLOCK) {
+ set_thread_flag(TIF_RESTART_SVC);
+ 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/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
diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
index 6b4fef8..503fd09 100644
--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -458,6 +458,8 @@ void do_signal(struct pt_regs *regs)
regs->psw.addr = restart_addr;
break;
case -ERESTART_RESTARTBLOCK:
+ /* if checkpointed here, set needs_restart */
+ set_thread_flag(TIF_RESTARTBLOCK);
regs->gprs[2] = -EINTR;
}
regs->svcnr = 0; /* Don't deal with this again. */
@@ -467,6 +469,10 @@ void do_signal(struct pt_regs *regs)
the debugger may change all our registers ... */
signr = get_signal_to_deliver(&info, &ka, regs, NULL);
+ /* we've passed the try_to_freeze() in get_signal_to_deliver(), won't
+ * be checkpointed before end of do_signal() */
+ clear_thread_flag(TIF_RESTARTBLOCK);
+
/* Depending on the signal settings we may need to revert the
decision to restart the system call. */
if (signr > 0 && regs->psw.addr == restart_addr) {
--
1.6.1
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