[PATCH v18 24/80] c/r: restart-blocks

[Oren Laadan <orenl@librato.com>]

(Paraphrasing what's said this message:
http://lists.openwall.net/linux-kernel/2007/12/05/64)

Restart blocks are callbacks used cause a system call to be restarted
with the arguments specified in the system call restart block. It is
useful for system call that are not idempotent, i.e. the argument(s)
might be a relative timeout, where some adjustments are required when
restarting the system call. It relies on the system call itself to set
up its restart point and the argument save area.  They are rare: an
actual signal would turn that it an EINTR. The only case that should
ever trigger this is some kernel action that interrupts the system
call, but does not actually result in any user-visible state changes -
like freeze and thaw.

So restart blocks are about time remaining for the system call to
sleep/wait. Generally in c/r, there are two possible time models that
we can follow: absolute, relative. Here, I chose to save the relative
timeout, measured from the beginning of the checkpoint. The time when
the checkpoint (and restart) begin is also saved. This information is
sufficient to restart in either model (absolute or negative).

Which model to use should eventually be a per application choice (and
possible configurable via cradvise() or some sort). For now, we adopt
the relative model, namely, at restart the timeout is set relative to
the beginning of the restart.

To checkpoint, we check if a task has a valid restart block, and if so
we save the *remaining* time that is has to wait/sleep, and the type
of the restart block.

To restart, we fill in the data required at the proper place in the
thread information. If the system call return an error (which is
possibly an -ERESTARTSYS eg), we not only use that error as our own
return value, but also arrange for the task to execute the signal
handler (by faking a signal). The handler, in turn, already has the
code to handle these restart request gracefully.

Changelog[v1]:
  - [Nathan Lynch] fix compilation errors with CONFIG_COMPAT=y

Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
---
 checkpoint/checkpoint.c          |    1 +
 checkpoint/process.c             |  226 ++++++++++++++++++++++++++++++++++++++
 checkpoint/restart.c             |    5 +-
 checkpoint/sys.c                 |    1 +
 include/linux/checkpoint.h       |    4 +
 include/linux/checkpoint_hdr.h   |   22 ++++
 include/linux/checkpoint_types.h |    3 +
 7 files changed, 260 insertions(+), 2 deletions(-)

diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index ad89f50..554400c 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -22,6 +22,7 @@
 #include <linux/mount.h>
 #include <linux/utsname.h>
 #include <linux/magic.h>
+#include <linux/hrtimer.h>
 #include <linux/checkpoint.h>
 #include <linux/checkpoint_hdr.h>
 
diff --git a/checkpoint/process.c b/checkpoint/process.c
index 1d1170c..330c8d4 100644
--- a/checkpoint/process.c
+++ b/checkpoint/process.c
@@ -12,6 +12,9 @@
 #define CKPT_DFLAG  CKPT_DSYS
 
 #include <linux/sched.h>
+#include <linux/posix-timers.h>
+#include <linux/futex.h>
+#include <linux/poll.h>
 #include <linux/checkpoint.h>
 #include <linux/checkpoint_hdr.h>
 
@@ -47,6 +50,116 @@ static int checkpoint_task_struct(struct ckpt_ctx *ctx, struct task_struct *t)
 	return ckpt_write_string(ctx, t->comm, TASK_COMM_LEN);
 }
 
+/* dump the task_struct of a given task */
+int checkpoint_restart_block(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+	struct ckpt_hdr_restart_block *h;
+	struct restart_block *restart_block;
+	long (*fn)(struct restart_block *);
+	s64 base, expire = 0;
+	int ret;
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_RESTART_BLOCK);
+	if (!h)
+		return -ENOMEM;
+
+	base = ktime_to_ns(ctx->ktime_begin);
+	restart_block = &task_thread_info(t)->restart_block;
+	fn = restart_block->fn;
+
+	/* FIX: enumerate clockid_t so we're immune to changes */
+
+	if (fn == do_no_restart_syscall) {
+
+		h->function_type = CKPT_RESTART_BLOCK_NONE;
+		ckpt_debug("restart_block: non\n");
+
+	} else if (fn == hrtimer_nanosleep_restart) {
+
+		h->function_type = CKPT_RESTART_BLOCK_HRTIMER_NANOSLEEP;
+		h->arg_0 = restart_block->nanosleep.index;
+		h->arg_1 = (unsigned long) restart_block->nanosleep.rmtp;
+		expire = restart_block->nanosleep.expires;
+		ckpt_debug("restart_block: hrtimer expire %lld now %lld\n",
+			 expire, base);
+
+	} else if (fn == posix_cpu_nsleep_restart) {
+		struct timespec ts;
+
+		h->function_type = CKPT_RESTART_BLOCK_POSIX_CPU_NANOSLEEP;
+		h->arg_0 = restart_block->arg0;
+		h->arg_1 = restart_block->arg1;
+		ts.tv_sec = restart_block->arg2;
+		ts.tv_nsec = restart_block->arg3;
+		expire = timespec_to_ns(&ts);
+		ckpt_debug("restart_block: posix_cpu expire %lld now %lld\n",
+			 expire, base);
+
+#ifdef CONFIG_COMPAT
+	} else if (fn == compat_nanosleep_restart) {
+
+		h->function_type = CKPT_RESTART_BLOCK_COMPAT_NANOSLEEP;
+		h->arg_0 = restart_block->nanosleep.index;
+		h->arg_1 = (unsigned long)restart_block->nanosleep.rmtp;
+		h->arg_2 = (unsigned long)restart_block->nanosleep.compat_rmtp;
+		expire = restart_block->nanosleep.expires;
+		ckpt_debug("restart_block: compat expire %lld now %lld\n",
+			 expire, base);
+
+	} else if (fn == compat_clock_nanosleep_restart) {
+
+		h->function_type = CKPT_RESTART_BLOCK_COMPAT_CLOCK_NANOSLEEP;
+		h->arg_0 = restart_block->nanosleep.index;
+		h->arg_1 = (unsigned long)restart_block->nanosleep.rmtp;
+		h->arg_2 = (unsigned long)restart_block->nanosleep.compat_rmtp;
+		expire = restart_block->nanosleep.expires;
+		ckpt_debug("restart_block: compat_clock expire %lld now %lld\n",
+			 expire, base);
+
+#endif
+	} else if (fn == futex_wait_restart) {
+
+		h->function_type = CKPT_RESTART_BLOCK_FUTEX;
+		h->arg_0 = (unsigned long) restart_block->futex.uaddr;
+		h->arg_1 = restart_block->futex.val;
+		h->arg_2 = restart_block->futex.flags;
+		h->arg_3 = restart_block->futex.bitset;
+		expire = restart_block->futex.time;
+		ckpt_debug("restart_block: futex expire %lld now %lld\n",
+			 expire, base);
+
+	} else if (fn == do_restart_poll) {
+		struct timespec ts;
+
+		h->function_type = CKPT_RESTART_BLOCK_POLL;
+		h->arg_0 = (unsigned long) restart_block->poll.ufds;
+		h->arg_1 = restart_block->poll.nfds;
+		h->arg_2 = restart_block->poll.has_timeout;
+		ts.tv_sec = restart_block->poll.tv_sec;
+		ts.tv_nsec = restart_block->poll.tv_nsec;
+		expire = timespec_to_ns(&ts);
+		ckpt_debug("restart_block: poll expire %lld now %lld\n",
+			 expire, base);
+
+	} else {
+
+		BUG();
+
+	}
+
+	/* common to all restart blocks: */
+	h->arg_4 = (base < expire ? expire - base : 0);
+
+	ckpt_debug("restart_block: args %#llx %#llx %#llx %#llx %#llx\n",
+		 h->arg_0, h->arg_1, h->arg_2, h->arg_3, h->arg_4);
+
+	ret = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+
+	ckpt_debug("restart_block ret %d\n", ret);
+	return ret;
+}
+
 /* dump the entire state of a given task */
 int checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
 {
@@ -63,6 +176,10 @@ int checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
 	ckpt_debug("thread %d\n", ret);
 	if (ret < 0)
 		goto out;
+	ret = checkpoint_restart_block(ctx, t);
+	ckpt_debug("restart-blocks %d\n", ret);
+	if (ret < 0)
+		goto out;
 	ret = checkpoint_cpu(ctx, t);
 	ckpt_debug("cpu %d\n", ret);
  out:
@@ -99,6 +216,111 @@ static int restore_task_struct(struct ckpt_ctx *ctx)
 	return ret;
 }
 
+int restore_restart_block(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_restart_block *h;
+	struct restart_block restart_block;
+	struct timespec ts;
+	clockid_t clockid;
+	s64 expire;
+	int ret = 0;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_RESTART_BLOCK);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	expire = ktime_to_ns(ctx->ktime_begin) + h->arg_4;
+	restart_block.fn = NULL;
+
+	ckpt_debug("restart_block: expire %lld begin %lld\n",
+		 expire, ktime_to_ns(ctx->ktime_begin));
+	ckpt_debug("restart_block: args %#llx %#llx %#llx %#llx %#llx\n",
+		 h->arg_0, h->arg_1, h->arg_2, h->arg_3, h->arg_4);
+
+	switch (h->function_type) {
+	case CKPT_RESTART_BLOCK_NONE:
+		restart_block.fn = do_no_restart_syscall;
+		break;
+	case CKPT_RESTART_BLOCK_HRTIMER_NANOSLEEP:
+		clockid = h->arg_0;
+		if (clockid < 0 || invalid_clockid(clockid))
+			break;
+		restart_block.fn = hrtimer_nanosleep_restart;
+		restart_block.nanosleep.index = clockid;
+		restart_block.nanosleep.rmtp =
+			(struct timespec __user *) (unsigned long) h->arg_1;
+		restart_block.nanosleep.expires = expire;
+		break;
+	case CKPT_RESTART_BLOCK_POSIX_CPU_NANOSLEEP:
+		clockid = h->arg_0;
+		if (clockid < 0 || invalid_clockid(clockid))
+			break;
+		restart_block.fn = posix_cpu_nsleep_restart;
+		restart_block.arg0 = clockid;
+		restart_block.arg1 = h->arg_1;
+		ts = ns_to_timespec(expire);
+		restart_block.arg2 = ts.tv_sec;
+		restart_block.arg3 = ts.tv_nsec;
+		break;
+#ifdef CONFIG_COMPAT
+	case CKPT_RESTART_BLOCK_COMPAT_NANOSLEEP:
+		clockid = h->arg_0;
+		if (clockid < 0 || invalid_clockid(clockid))
+			break;
+		restart_block.fn = compat_nanosleep_restart;
+		restart_block.nanosleep.index = clockid;
+		restart_block.nanosleep.rmtp =
+			(struct timespec __user *) (unsigned long) h->arg_1;
+		restart_block.nanosleep.compat_rmtp =
+			(struct compat_timespec __user *)
+				(unsigned long) h->arg_2;
+		restart_block.nanosleep.expires = expire;
+		break;
+	case CKPT_RESTART_BLOCK_COMPAT_CLOCK_NANOSLEEP:
+		clockid = h->arg_0;
+		if (clockid < 0 || invalid_clockid(clockid))
+			break;
+		restart_block.fn = compat_clock_nanosleep_restart;
+		restart_block.nanosleep.index = clockid;
+		restart_block.nanosleep.rmtp =
+			(struct timespec __user *) (unsigned long) h->arg_1;
+		restart_block.nanosleep.compat_rmtp =
+			(struct compat_timespec __user *)
+				(unsigned long) h->arg_2;
+		restart_block.nanosleep.expires = expire;
+		break;
+#endif
+	case CKPT_RESTART_BLOCK_FUTEX:
+		restart_block.fn = futex_wait_restart;
+		restart_block.futex.uaddr = (u32 *) (unsigned long) h->arg_0;
+		restart_block.futex.val = h->arg_1;
+		restart_block.futex.flags = h->arg_2;
+		restart_block.futex.bitset = h->arg_3;
+		restart_block.futex.time = expire;
+		break;
+	case CKPT_RESTART_BLOCK_POLL:
+		restart_block.fn = do_restart_poll;
+		restart_block.poll.ufds =
+			(struct pollfd __user *) (unsigned long) h->arg_0;
+		restart_block.poll.nfds = h->arg_1;
+		restart_block.poll.has_timeout = h->arg_2;
+		ts = ns_to_timespec(expire);
+		restart_block.poll.tv_sec = ts.tv_sec;
+		restart_block.poll.tv_nsec = ts.tv_nsec;
+		break;
+	default:
+		break;
+	}
+
+	if (restart_block.fn)
+		task_thread_info(current)->restart_block = restart_block;
+	else
+		ret = -EINVAL;
+
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
 /* read the entire state of the current task */
 int restore_task(struct ckpt_ctx *ctx)
 {
@@ -112,6 +334,10 @@ int restore_task(struct ckpt_ctx *ctx)
 	ckpt_debug("thread %d\n", ret);
 	if (ret < 0)
 		goto out;
+	ret = restore_restart_block(ctx);
+	ckpt_debug("restart-blocks %d\n", ret);
+	if (ret < 0)
+		goto out;
 	ret = restore_cpu(ctx);
 	ckpt_debug("cpu %d\n", ret);
  out:
diff --git a/checkpoint/restart.c b/checkpoint/restart.c
index cb02ffb..fdad264 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -16,6 +16,8 @@
 #include <linux/file.h>
 #include <linux/magic.h>
 #include <linux/utsname.h>
+#include <asm/syscall.h>
+#include <linux/elf.h>
 #include <linux/checkpoint.h>
 #include <linux/checkpoint_hdr.h>
 
@@ -482,6 +484,5 @@ long do_restart(struct ckpt_ctx *ctx, pid_t pid)
 	if (ret < 0)
 		return ret;
 
-	/* on success, adjust the return value if needed [TODO] */
-	return restore_retval(ctx);
+	return restore_retval();
 }
diff --git a/checkpoint/sys.c b/checkpoint/sys.c
index dda2c21..b37bc8c 100644
--- a/checkpoint/sys.c
+++ b/checkpoint/sys.c
@@ -193,6 +193,7 @@ static struct ckpt_ctx *ckpt_ctx_alloc(int fd, unsigned long uflags,
 
 	ctx->uflags = uflags;
 	ctx->kflags = kflags;
+	ctx->ktime_begin = ktime_get();
 
 	err = -EBADF;
 	ctx->file = fget(fd);
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index aa8ce11..14c0a7f 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -70,6 +70,10 @@ extern int restore_read_header_arch(struct ckpt_ctx *ctx);
 extern int restore_thread(struct ckpt_ctx *ctx);
 extern int restore_cpu(struct ckpt_ctx *ctx);
 
+extern int checkpoint_restart_block(struct ckpt_ctx *ctx,
+				    struct task_struct *t);
+extern int restore_restart_block(struct ckpt_ctx *ctx);
+
 static inline int ckpt_validate_errno(int errno)
 {
 	return (errno >= 0) && (errno < MAX_ERRNO);
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 92d082e..b72c59c 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -52,6 +52,7 @@ enum {
 	CKPT_HDR_STRING,
 
 	CKPT_HDR_TASK = 101,
+	CKPT_HDR_RESTART_BLOCK,
 	CKPT_HDR_THREAD,
 	CKPT_HDR_CPU,
 
@@ -122,4 +123,25 @@ struct ckpt_hdr_task {
 	__u64 clear_child_tid;
 } __attribute__((aligned(8)));
 
+/* restart blocks */
+struct ckpt_hdr_restart_block {
+	struct ckpt_hdr h;
+	__u64 function_type;
+	__u64 arg_0;
+	__u64 arg_1;
+	__u64 arg_2;
+	__u64 arg_3;
+	__u64 arg_4;
+} __attribute__((aligned(8)));
+
+enum restart_block_type {
+	CKPT_RESTART_BLOCK_NONE = 1,
+	CKPT_RESTART_BLOCK_HRTIMER_NANOSLEEP,
+	CKPT_RESTART_BLOCK_POSIX_CPU_NANOSLEEP,
+	CKPT_RESTART_BLOCK_COMPAT_NANOSLEEP,
+	CKPT_RESTART_BLOCK_COMPAT_CLOCK_NANOSLEEP,
+	CKPT_RESTART_BLOCK_POLL,
+	CKPT_RESTART_BLOCK_FUTEX
+};
+
 #endif /* _CHECKPOINT_CKPT_HDR_H_ */
diff --git a/include/linux/checkpoint_types.h b/include/linux/checkpoint_types.h
index 15dbe1b..046bdc4 100644
--- a/include/linux/checkpoint_types.h
+++ b/include/linux/checkpoint_types.h
@@ -15,10 +15,13 @@
 #include <linux/sched.h>
 #include <linux/nsproxy.h>
 #include <linux/fs.h>
+#include <linux/ktime.h>
 
 struct ckpt_ctx {
 	int crid;		/* unique checkpoint id */
 
+	ktime_t ktime_begin;	/* checkpoint start time */
+
 	pid_t root_pid;				/* [container] root pid */
 	struct task_struct *root_task;		/* [container] root task */
 	struct nsproxy *root_nsproxy;		/* [container] root nsproxy */
-- 
1.6.0.4

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