[PATCH 0/5] linux-cr: make pids a proper shared object

[PATCH 0/5] linux-cr: make pids a proper shared object

[Oren Laadan]

Hi,

This patch-set changes the way pids are saved/restored to treat them
as proper shared objects (tracked in objhash) rather than simple pid
numbers. The patch-set applies on top of branch 'ckpt-v23-rc1'. It
also requires updates to user-cr (patchset posted separately).

Thanks,

Oren.

[PATCH 1/5] c/r: introduce ckpt_task_vnr(), ckpt_pid_vnr()

[Oren Laadan]

This helpoer is Useful to get the pid from the root task's (checkpoint
or restart) point of view.

Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 include/linux/checkpoint.h     |   10 +++++++++-
 kernel/checkpoint/checkpoint.c |    5 +++--
 kernel/checkpoint/restart.c    |    6 ++----
 kernel/signal.c                |    2 +-
 4 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index c015106..fe61edb 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -110,8 +110,16 @@ extern int checkpoint_dump_page(struct ckpt_ctx *ctx, struct page *page);
 extern int restore_read_page(struct ckpt_ctx *ctx, struct page *page);
 
 /* pids */
-extern pid_t ckpt_pid_nr(struct ckpt_ctx *ctx, struct pid *pid);
 extern struct pid *_ckpt_find_pgrp(struct ckpt_ctx *ctx, pid_t pgid);
+static inline pid_t ckpt_task_vnr(struct ckpt_ctx *ctx, struct task_struct *task)
+{
+	return task_pid_nr_ns(task, ctx->root_nsproxy->pid_ns);
+}
+static inline pid_t ckpt_pid_vnr(struct ckpt_ctx *ctx, struct pid *pid)
+{
+	return pid_nr_ns(pid, ctx->root_nsproxy->pid_ns);
+}
+extern int ckpt_lookup_pid(struct ckpt_ctx *ctx, struct pid *pid);
 
 /* defined in objhash.c and also used in security/security.c */
 extern void lsm_string_free(struct kref *kref);
diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
index 0f46acf..7cd491b 100644
--- a/kernel/checkpoint/checkpoint.c
+++ b/kernel/checkpoint/checkpoint.c
@@ -28,6 +28,7 @@
 #include <linux/hrtimer.h>
 #include <linux/deferqueue.h>
 #include <linux/checkpoint.h>
+#include <linux/flex_array.h>
 #include <linux/pid_namespace.h>
 
 /* unique checkpoint identifier (FIXME: should be per-container ?) */
@@ -243,10 +244,10 @@ static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
 {
 	struct task_struct *root = ctx->root_task;
 	struct nsproxy *nsproxy;
-	int ret = 0;
 	struct pid_namespace *pidns;
+	int ret = 0;
 
-	ckpt_debug("check %d\n", task_pid_nr_ns(t, ctx->root_nsproxy->pid_ns));
+	ckpt_debug("check %d\n", ckpt_task_vnr(ctx, t));
 
 	if (t->exit_state == EXIT_DEAD) {
 		_ckpt_err(ctx, -EBUSY, "%(T)Task state EXIT_DEAD\n");
diff --git a/kernel/checkpoint/restart.c b/kernel/checkpoint/restart.c
index 2eae499..e844568 100644
--- a/kernel/checkpoint/restart.c
+++ b/kernel/checkpoint/restart.c
@@ -913,8 +913,7 @@ static int wait_task_active(struct ckpt_ctx *ctx)
 
 static int wait_task_sync(struct ckpt_ctx *ctx)
 {
-	ckpt_debug("pid %d syncing\n",
-		task_pid_nr_ns(current, task_active_pid_ns(ctx->root_task)));
+	ckpt_debug("pid %d syncing\n", ckpt_task_vnr(ctx, current));
 	wait_event_interruptible(ctx->waitq, ckpt_test_complete(ctx));
 	ckpt_debug("task sync done (errno %d)\n", ctx->errno);
 	if (ckpt_test_error(ctx))
@@ -1187,10 +1186,9 @@ static struct task_struct *choose_root_task(struct ckpt_ctx *ctx, pid_t pid)
 
 	read_lock(&tasklist_lock);
 	list_for_each_entry(task, &current->children, sibling) {
-		if (task_pid_nr_ns(task, ctx->coord_pidns) == pid) {
+		if (task_pid_vnr(task) == pid) {
 			get_task_struct(task);
 			ctx->root_task = task;
-			ctx->root_pid = pid;
 			break;
 		}
 	}
diff --git a/kernel/signal.c b/kernel/signal.c
index b1e6a31..dca40be 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3352,7 +3352,7 @@ static int restore_signal(struct ckpt_ctx *ctx)
 			 * fail, so no need for explicit test
 			 */
 			ret = do_tiocspgrp(tty, tty_pair_get_tty(tty),
-					   h->tty_pgrp);
+					   pid_vnr(pgrp));
 			if (ret < 0)
 				goto out;
 		}
-- 
1.7.1

Re: [PATCH 1/5] c/r: introduce ckpt_task_vnr(), ckpt_pid_vnr()

[Oren Laadan]

Hmmm.. the cover post did not make it :(

This patch-set changes the way pids are handled in c/r - instead
of simple pid numbers, we now treat them as proper shared objects.

The patch applies on top of the most recent branch 'ckpt-v23-rc1' 
of c/r (for 2.6.37 kernel).

Thanks,

Oren.

On 01/26/2011 11:10 AM, Oren Laadan wrote:
> This helpoer is Useful to get the pid from the root task's (checkpoint
> or restart) point of view.
> 
> Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
> ---
>  include/linux/checkpoint.h     |   10 +++++++++-
>  kernel/checkpoint/checkpoint.c |    5 +++--
>  kernel/checkpoint/restart.c    |    6 ++----
>  kernel/signal.c                |    2 +-
>  4 files changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
> index c015106..fe61edb 100644
> --- a/include/linux/checkpoint.h
> +++ b/include/linux/checkpoint.h
> @@ -110,8 +110,16 @@ extern int checkpoint_dump_page(struct ckpt_ctx *ctx, struct page *page);
>  extern int restore_read_page(struct ckpt_ctx *ctx, struct page *page);
>  
>  /* pids */
> -extern pid_t ckpt_pid_nr(struct ckpt_ctx *ctx, struct pid *pid);
>  extern struct pid *_ckpt_find_pgrp(struct ckpt_ctx *ctx, pid_t pgid);
> +static inline pid_t ckpt_task_vnr(struct ckpt_ctx *ctx, struct task_struct *task)
> +{
> +	return task_pid_nr_ns(task, ctx->root_nsproxy->pid_ns);
> +}
> +static inline pid_t ckpt_pid_vnr(struct ckpt_ctx *ctx, struct pid *pid)
> +{
> +	return pid_nr_ns(pid, ctx->root_nsproxy->pid_ns);
> +}
> +extern int ckpt_lookup_pid(struct ckpt_ctx *ctx, struct pid *pid);
>  
>  /* defined in objhash.c and also used in security/security.c */
>  extern void lsm_string_free(struct kref *kref);
> diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
> index 0f46acf..7cd491b 100644
> --- a/kernel/checkpoint/checkpoint.c
> +++ b/kernel/checkpoint/checkpoint.c
> @@ -28,6 +28,7 @@
>  #include <linux/hrtimer.h>
>  #include <linux/deferqueue.h>
>  #include <linux/checkpoint.h>
> +#include <linux/flex_array.h>
>  #include <linux/pid_namespace.h>
>  
>  /* unique checkpoint identifier (FIXME: should be per-container ?) */
> @@ -243,10 +244,10 @@ static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
>  {
>  	struct task_struct *root = ctx->root_task;
>  	struct nsproxy *nsproxy;
> -	int ret = 0;
>  	struct pid_namespace *pidns;
> +	int ret = 0;
>  
> -	ckpt_debug("check %d\n", task_pid_nr_ns(t, ctx->root_nsproxy->pid_ns));
> +	ckpt_debug("check %d\n", ckpt_task_vnr(ctx, t));
>  
>  	if (t->exit_state == EXIT_DEAD) {
>  		_ckpt_err(ctx, -EBUSY, "%(T)Task state EXIT_DEAD\n");
> diff --git a/kernel/checkpoint/restart.c b/kernel/checkpoint/restart.c
> index 2eae499..e844568 100644
> --- a/kernel/checkpoint/restart.c
> +++ b/kernel/checkpoint/restart.c
> @@ -913,8 +913,7 @@ static int wait_task_active(struct ckpt_ctx *ctx)
>  
>  static int wait_task_sync(struct ckpt_ctx *ctx)
>  {
> -	ckpt_debug("pid %d syncing\n",
> -		task_pid_nr_ns(current, task_active_pid_ns(ctx->root_task)));
> +	ckpt_debug("pid %d syncing\n", ckpt_task_vnr(ctx, current));
>  	wait_event_interruptible(ctx->waitq, ckpt_test_complete(ctx));
>  	ckpt_debug("task sync done (errno %d)\n", ctx->errno);
>  	if (ckpt_test_error(ctx))
> @@ -1187,10 +1186,9 @@ static struct task_struct *choose_root_task(struct ckpt_ctx *ctx, pid_t pid)
>  
>  	read_lock(&tasklist_lock);
>  	list_for_each_entry(task, &current->children, sibling) {
> -		if (task_pid_nr_ns(task, ctx->coord_pidns) == pid) {
> +		if (task_pid_vnr(task) == pid) {
>  			get_task_struct(task);
>  			ctx->root_task = task;
> -			ctx->root_pid = pid;
>  			break;
>  		}
>  	}
> diff --git a/kernel/signal.c b/kernel/signal.c
> index b1e6a31..dca40be 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -3352,7 +3352,7 @@ static int restore_signal(struct ckpt_ctx *ctx)
>  			 * fail, so no need for explicit test
>  			 */
>  			ret = do_tiocspgrp(tty, tty_pair_get_tty(tty),
> -					   h->tty_pgrp);
> +					   pid_vnr(pgrp));
>  			if (ret < 0)
>  				goto out;
>  		}

Re: [PATCH 1/5] c/r: introduce ckpt_task_vnr(), ckpt_pid_vnr()

[Oren Laadan]

Note that you also need to apply the corresponding user-cr patchset
to sync the userspace tools with this new logic.

Oren.

On 01/26/2011 11:20 AM, Oren Laadan wrote:
> 
> Hmmm.. the cover post did not make it :(
> 
> This patch-set changes the way pids are handled in c/r - instead
> of simple pid numbers, we now treat them as proper shared objects.
> 
> The patch applies on top of the most recent branch 'ckpt-v23-rc1' 
> of c/r (for 2.6.37 kernel).
> 
> Thanks,
> 
> Oren.
> 
> On 01/26/2011 11:10 AM, Oren Laadan wrote:
>> This helpoer is Useful to get the pid from the root task's (checkpoint
>> or restart) point of view.
>>
>> Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
>> ---
>>  include/linux/checkpoint.h     |   10 +++++++++-
>>  kernel/checkpoint/checkpoint.c |    5 +++--
>>  kernel/checkpoint/restart.c    |    6 ++----
>>  kernel/signal.c                |    2 +-
>>  4 files changed, 15 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
>> index c015106..fe61edb 100644
>> --- a/include/linux/checkpoint.h
>> +++ b/include/linux/checkpoint.h
>> @@ -110,8 +110,16 @@ extern int checkpoint_dump_page(struct ckpt_ctx *ctx, struct page *page);
>>  extern int restore_read_page(struct ckpt_ctx *ctx, struct page *page);
>>  
>>  /* pids */
>> -extern pid_t ckpt_pid_nr(struct ckpt_ctx *ctx, struct pid *pid);
>>  extern struct pid *_ckpt_find_pgrp(struct ckpt_ctx *ctx, pid_t pgid);
>> +static inline pid_t ckpt_task_vnr(struct ckpt_ctx *ctx, struct task_struct *task)
>> +{
>> +	return task_pid_nr_ns(task, ctx->root_nsproxy->pid_ns);
>> +}
>> +static inline pid_t ckpt_pid_vnr(struct ckpt_ctx *ctx, struct pid *pid)
>> +{
>> +	return pid_nr_ns(pid, ctx->root_nsproxy->pid_ns);
>> +}
>> +extern int ckpt_lookup_pid(struct ckpt_ctx *ctx, struct pid *pid);
>>  
>>  /* defined in objhash.c and also used in security/security.c */
>>  extern void lsm_string_free(struct kref *kref);
>> diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
>> index 0f46acf..7cd491b 100644
>> --- a/kernel/checkpoint/checkpoint.c
>> +++ b/kernel/checkpoint/checkpoint.c
>> @@ -28,6 +28,7 @@
>>  #include <linux/hrtimer.h>
>>  #include <linux/deferqueue.h>
>>  #include <linux/checkpoint.h>
>> +#include <linux/flex_array.h>
>>  #include <linux/pid_namespace.h>
>>  
>>  /* unique checkpoint identifier (FIXME: should be per-container ?) */
>> @@ -243,10 +244,10 @@ static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
>>  {
>>  	struct task_struct *root = ctx->root_task;
>>  	struct nsproxy *nsproxy;
>> -	int ret = 0;
>>  	struct pid_namespace *pidns;
>> +	int ret = 0;
>>  
>> -	ckpt_debug("check %d\n", task_pid_nr_ns(t, ctx->root_nsproxy->pid_ns));
>> +	ckpt_debug("check %d\n", ckpt_task_vnr(ctx, t));
>>  
>>  	if (t->exit_state == EXIT_DEAD) {
>>  		_ckpt_err(ctx, -EBUSY, "%(T)Task state EXIT_DEAD\n");
>> diff --git a/kernel/checkpoint/restart.c b/kernel/checkpoint/restart.c
>> index 2eae499..e844568 100644
>> --- a/kernel/checkpoint/restart.c
>> +++ b/kernel/checkpoint/restart.c
>> @@ -913,8 +913,7 @@ static int wait_task_active(struct ckpt_ctx *ctx)
>>  
>>  static int wait_task_sync(struct ckpt_ctx *ctx)
>>  {
>> -	ckpt_debug("pid %d syncing\n",
>> -		task_pid_nr_ns(current, task_active_pid_ns(ctx->root_task)));
>> +	ckpt_debug("pid %d syncing\n", ckpt_task_vnr(ctx, current));
>>  	wait_event_interruptible(ctx->waitq, ckpt_test_complete(ctx));
>>  	ckpt_debug("task sync done (errno %d)\n", ctx->errno);
>>  	if (ckpt_test_error(ctx))
>> @@ -1187,10 +1186,9 @@ static struct task_struct *choose_root_task(struct ckpt_ctx *ctx, pid_t pid)
>>  
>>  	read_lock(&tasklist_lock);
>>  	list_for_each_entry(task, &current->children, sibling) {
>> -		if (task_pid_nr_ns(task, ctx->coord_pidns) == pid) {
>> +		if (task_pid_vnr(task) == pid) {
>>  			get_task_struct(task);
>>  			ctx->root_task = task;
>> -			ctx->root_pid = pid;
>>  			break;
>>  		}
>>  	}
>> diff --git a/kernel/signal.c b/kernel/signal.c
>> index b1e6a31..dca40be 100644
>> --- a/kernel/signal.c
>> +++ b/kernel/signal.c
>> @@ -3352,7 +3352,7 @@ static int restore_signal(struct ckpt_ctx *ctx)
>>  			 * fail, so no need for explicit test
>>  			 */
>>  			ret = do_tiocspgrp(tty, tty_pair_get_tty(tty),
>> -					   h->tty_pgrp);
>> +					   pid_vnr(pgrp));
>>  			if (ret < 0)
>>  				goto out;
>>  		}
> 

[PATCH 2/5] c/r: nit to avoid rcu lockdep complaint in restore_obj_sighand()

[Oren Laadan]

Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 kernel/signal.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index dca40be..3842f5d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2871,7 +2871,7 @@ static void *restore_sighand(struct ckpt_ctx *ctx)
 int restore_obj_sighand(struct ckpt_ctx *ctx, int sighand_objref)
 {
 	struct sighand_struct *sighand;
-	struct sighand_struct *old_sighand;
+	struct sighand_struct *old_sighand = NULL;
 
 	sighand = ckpt_obj_fetch(ctx, sighand_objref, CKPT_OBJ_SIGHAND);
 	if (IS_ERR(sighand))
@@ -2884,11 +2884,14 @@ int restore_obj_sighand(struct ckpt_ctx *ctx, int sighand_objref)
 
 	/* manipulate tsk->sighand with tasklist lock write-held */
 	write_lock_irq(&tasklist_lock);
-	old_sighand = rcu_dereference(current->sighand);
+	old_sighand = rcu_dereference_check(current->sighand,
+					    rcu_read_lock_held() ||
+					    lockdep_is_held(&tasklist_lock));
 	spin_lock(&old_sighand->siglock);
 	rcu_assign_pointer(current->sighand, sighand);
 	spin_unlock(&old_sighand->siglock);
 	write_unlock_irq(&tasklist_lock);
+
 	__cleanup_sighand(old_sighand);
 
 	return 0;
-- 
1.7.1

[PATCH 3/5] c/r: [PIDS 1/3] introduce pids objects

[Oren Laadan]

Add the interface to handle pids as proper c/r shared objects.  This
is the first step in converting the c/r code to hanlde pid as pids
objects that are namespace aware. Also remote the unused field
@root_pid from struct ckpt_ctx.

Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 include/linux/checkpoint_hdr.h   |    6 +++++-
 include/linux/checkpoint_types.h |    1 -
 kernel/checkpoint/checkpoint.c   |    2 --
 kernel/checkpoint/restart.c      |    1 -
 kernel/pid.c                     |   28 ++++++++++++++++++++++++++++
 5 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index b12d586..922eff0 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -245,6 +245,8 @@ struct ckpt_hdr_objref {
 enum obj_type {
 	CKPT_OBJ_IGNORE = 0,
 #define CKPT_OBJ_IGNORE CKPT_OBJ_IGNORE
+	CKPT_OBJ_PID,
+#define CKPT_OBJ_PID CKPT_OBJ_PID
 	CKPT_OBJ_INODE,
 #define CKPT_OBJ_INODE CKPT_OBJ_INODE
 	CKPT_OBJ_FILE_TABLE,
@@ -373,7 +375,9 @@ struct ckpt_pids {
 } __attribute__((aligned(8)));
 
 /* pids */
-#define CKPT_PID_NULL  -1
+/* (negative but not valid error) */
+#define CKPT_PID_NULL  (-4096)  /* null pid pointer */
+#define CKPT_PID_ROOT  (-4097)  /* pid same as root task */
 
 /* task data */
 struct ckpt_hdr_task {
diff --git a/include/linux/checkpoint_types.h b/include/linux/checkpoint_types.h
index cf74d3e..87a569a 100644
--- a/include/linux/checkpoint_types.h
+++ b/include/linux/checkpoint_types.h
@@ -35,7 +35,6 @@ struct ckpt_ctx {
 	ktime_t ktime_begin;		/* operation start time */
 
 	int root_init;				/* [container] root init ? */
-	pid_t root_pid;				/* [container] root pid */
 	struct task_struct *root_task;		/* [container] root task */
 	struct nsproxy *root_nsproxy;		/* [container] root nsproxy */
 	struct task_struct *root_freezer;	/* [container] root task */
diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
index 7cd491b..42de30a 100644
--- a/kernel/checkpoint/checkpoint.c
+++ b/kernel/checkpoint/checkpoint.c
@@ -629,8 +629,6 @@ static int init_checkpoint_ctx(struct ckpt_ctx *ctx, pid_t pid)
 	 * occurs then ckpt_ctx_free() is eventually called.
 	 */
 
-	ctx->root_pid = pid;
-
 	/* root task */
 	rcu_read_lock();
 	task = find_task_by_vpid(pid);
diff --git a/kernel/checkpoint/restart.c b/kernel/checkpoint/restart.c
index e844568..adcfb23 100644
--- a/kernel/checkpoint/restart.c
+++ b/kernel/checkpoint/restart.c
@@ -1178,7 +1178,6 @@ static struct task_struct *choose_root_task(struct ckpt_ctx *ctx, pid_t pid)
 	struct task_struct *task;
 
 	if (ctx->uflags & RESTART_TASKSELF) {
-		ctx->root_pid = pid;
 		ctx->root_task = current;
 		get_task_struct(current);
 		return current;
diff --git a/kernel/pid.c b/kernel/pid.c
index f08f40a..0269991 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -36,6 +36,7 @@
 #include <linux/pid_namespace.h>
 #include <linux/init_task.h>
 #include <linux/syscalls.h>
+#include <linux/checkpoint.h>
 
 #define pid_hashfn(nr, ns)	\
 	hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
@@ -571,6 +572,30 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
 	return pid;
 }
 
+#ifdef CONFIG_CHECKPOINT
+
+/* pid-related checkpoint objects */
+
+static int obj_pid_grab(void *ptr)
+{
+	get_pid((struct pid *) ptr);
+	return 0;
+}
+
+static void obj_pid_drop(void *ptr, int lastref)
+{
+	put_pid((struct pid *) ptr);
+}
+
+static const struct ckpt_obj_ops ckpt_obj_pid_ops = {
+	.obj_name = "PID",
+	.obj_type = CKPT_OBJ_PID,
+	.ref_drop = obj_pid_drop,
+	.ref_grab = obj_pid_grab,
+};
+
+#endif /* CONFIG_CHECKPOINT */
+
 /*
  * The pid hash table is scaled according to the amount of memory in the
  * machine.  From a minimum of 16 slots up to 4096 slots at one gigabyte or
@@ -605,4 +630,7 @@ void __init pidmap_init(void)
 
 	init_pid_ns.pid_cachep = KMEM_CACHE(pid,
 			SLAB_HWCACHE_ALIGN | SLAB_PANIC);
+#ifdef CONFIG_CHECKPOINT
+	register_checkpoint_obj(&ckpt_obj_pid_ops);
+#endif
 }
-- 
1.7.1

[PATCH 4/5] c/r: checkpoint and restart pids objects

[Oren Laadan]

Make use of (shared) pids objects instead of simply saving the pid_t
numbers in both checkpoint and restart.

The motivation for this change is twofold. First, since pid-ns came to
life pid's in the kenrel _are_ shared objects and should be treated as
such. This is useful e.g. for tty handling and also file-ownership
(the latter waiting for this feature). Second, to properly support
nested namesapces we need to report with each pid the entire list of
pid numbers, not only a single pid. While current we do that for all
"live" pids (those that belong to live tasks), we didn't do it for
"dead" pids (to be assigned to ghost restarting tasks).

Note, that ideally the list of vpids of a pid object should also
include the pid-ns to which each level belongs; however, in this patch
we don't yet hanlde that. So only linear pid-nesting works well and
not arbitrary tree.

DICLAIMER: this patch is big and intrusive!  Here is a summary of the
changes that it makes:

CHECKPOINT:

1) Modified the data structures used to describe pids and tasks' pids:
 struct ckpt_pids - for the data of a pids object (depth, numbers)
   (pids objects are collected in the order found, and are assigned
   tags sequentially, starting from 1)
 struct ckpt_task_pids - for a task's pids, holding the _tag_ of the
   corresponding pids object rather than their pid numbers themselves.

2) Accordingly, two arrays are used to hold this information:
 ctx->pids_arr - array of 'struct ckpt_pids' collected from the tasks
   and the pids they reference. Entries are of variable size depending
   on the pid-ns nesting level.
 ctx->tasks_arr - array of 'struct ckpt_task_pids' collected from teh
   tasks. Entries are of fixed size, and hold the objref tags to the
 shared pids objects rather than actual pid numbers.
 (the old vpids_arr is no longer needed, nor written separately).

3) We now first write the pids information, then tasks' pids.

4) checkpoint_pids() builds and writes the ctx->pids_arr:
 checkpoint_pids_build() - iterates over the tasks and collects the
   unique pids in a flex_array (also inserts them into the objhash)
 checkpoint_pids_dumps() - dumps the data from the flex_array in
   the format of ctx->tasks_arr

5) checkpoint_tree() dumps the tasks' pids information, by scanning
 all the tasks and writing out tags of the pids they reference. If
 a pgid/sid is zero, i.e. from an ancestor pid-ns, then the tag will
 be zero.

6) In container checkpoint, pids out of our namesapce are disallwed.
 We don't do leak detection on pids objects (should we ?).

RESTART:

1) We first call prepare_descendants() to set the ->checkpoint_ctx
 of the restarting tasks, and _then_ read the pids data followed by
 the tasks' pids data. We validate both against existing tasks.

2) restore_read_pids() reads the pids data, validates that each pid
 exists (*) and adds the pids to the objhash. Verify that the owner
 task is within our restart context.

(*) We validate them from the root task's point of view, by seeing
 that the task has the correct 'struct pid' pointer. NOTE: user-cr
 does not support restart --no-pids when there are nested pis-ns,
 because is it quite complicated to find ou the pids of all tasks
 at all nested levels from userspace.

3) restore_read_tasks() reads the tasks' pids data, validates each
 task and adds it to the ctx->tasks_arr. Verify that the task is
 within our restart context.

4) We track the array of restarting _tasks_ and the active _task_
 instead an array of restarting pids and the active pid. The helpers
 to wake-up, sync, check active task etc were modified accordingly.
 It improves and simplifies the logic, e.g. restore_activate_next().

5) There are two special values for pgid/sid tags:
 0 - means that it is from an ancestor namespace, so we verify that
   this is the case. For sid, user-cr should have created the task
   properly; for pgid, use the coordinator's (or coordinator's parent)
   pid if from differnet namespace, or fail.
 CKPT_PID_ROOT - means that we want to reuse the root task's sid,
   useful for when the root task is _not_ a conatiner init (e.g. in
   subtree c/r) and its session (like our pgrp) was inherited from
   somewhere above).

6) Restoring of a task's pgid was moved to when task is validated,
 as this should be part of the validation.

NOTE: the patch does not yet allow non-linear nesting of pid-ns.
This would require to make pid-ns a shared object and track it by
the 'struct ckpt_pids' on the kernel side, and in userspace we'll
need to update the logic of MakeForest algorithm to be pid-ns aware
(probably similarly to how sid constraints are handled).

Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 include/linux/checkpoint_hdr.h   |   22 ++-
 include/linux/checkpoint_types.h |   10 +-
 kernel/checkpoint/checkpoint.c   |  440 +++++++++++++++++++++----------
 kernel/checkpoint/process.c      |  108 +-------
 kernel/checkpoint/restart.c      |  551 ++++++++++++++++++++++++++++++--------
 kernel/checkpoint/sys.c          |    5 -
 6 files changed, 773 insertions(+), 363 deletions(-)

diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 922eff0..c0a548a 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -107,7 +107,9 @@ enum {
 	CKPT_HDR_SECURITY,
 #define CKPT_HDR_SECURITY CKPT_HDR_SECURITY
 
-	CKPT_HDR_TREE = 101,
+	CKPT_HDR_PIDS = 101,
+#define CKPT_HDR_PIDS CKPT_HDR_PIDS
+	CKPT_HDR_TREE,
 #define CKPT_HDR_TREE CKPT_HDR_TREE
 	CKPT_HDR_TASK,
 #define CKPT_HDR_TASK CKPT_HDR_TASK
@@ -358,20 +360,32 @@ struct ckpt_hdr_container {
 	 */
 } __attribute__((aligned(8)));;
 
+/* pids array */
+struct ckpt_hdr_pids {
+	struct ckpt_hdr h;
+	__u32 nr_pids;
+	__u32 nr_vpids;
+} __attribute__((aligned(8)));
+
+struct ckpt_pids {
+	__u32 depth;
+	__s32 numbers[1];
+} __attribute__((aligned(8)));
+
 /* task tree */
 struct ckpt_hdr_tree {
 	struct ckpt_hdr h;
-	__s32 nr_tasks;
+	__u32 nr_tasks;
 } __attribute__((aligned(8)));
 
-struct ckpt_pids {
+struct ckpt_task_pids {
 	/* These pids are in the root_nsproxy's pid ns */
 	__s32 vpid;
 	__s32 vppid;
 	__s32 vtgid;
 	__s32 vpgid;
 	__s32 vsid;
-	__s32 depth; /* pid namespace depth relative to container init */
+	__u32 depth;
 } __attribute__((aligned(8)));
 
 /* pids */
diff --git a/include/linux/checkpoint_types.h b/include/linux/checkpoint_types.h
index 87a569a..60c664f 100644
--- a/include/linux/checkpoint_types.h
+++ b/include/linux/checkpoint_types.h
@@ -68,16 +68,14 @@ struct ckpt_ctx {
 
 	int nr_vpids;			/* total count of vpids */
 
-	/* [checkpoint] */
-	struct task_struct *tsk;	/* current target task */
 	struct task_struct **tasks_arr;	/* array of all tasks */
 	int nr_tasks;			/* size of tasks array */
 
+	/* [checkpoint] */
+	struct task_struct *tsk;	/* current target task */
+
 	/* [restart] */
-	struct pid_namespace *coord_pidns;/* coordinator pid_ns */
-	struct ckpt_pids *pids_arr;	/* array of all pids [restart] */
-	int nr_pids;			/* size of pids array */
-	int active_pid;			/* (next) position in pids array */
+	int active_task;		/* (next) position in pids array */
 	atomic_t nr_total;		/* total tasks count */
 	struct completion complete;	/* completion for container root */
 	wait_queue_head_t waitq;	/* waitqueue for restarting tasks */
diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
index 42de30a..f351f49 100644
--- a/kernel/checkpoint/checkpoint.c
+++ b/kernel/checkpoint/checkpoint.c
@@ -313,133 +313,6 @@ static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
 	return ret;
 }
 
-#define CKPT_HDR_PIDS_CHUNK	256
-
-/*
- * Write the pids in ctx->root_nsproxy->pidns.  This info is
- * needed at restart to unambiguously dereference tasks.
- */
-static int checkpoint_pids(struct ckpt_ctx *ctx)
-{
-	struct ckpt_pids *h;
-	struct pid_namespace *root_pidns;
-	struct task_struct *task;
-	struct task_struct **tasks_arr;
-	int nr_tasks, n, pos = 0, ret = 0;
-
-	root_pidns = ctx->root_nsproxy->pid_ns;
-	tasks_arr = ctx->tasks_arr;
-	nr_tasks = ctx->nr_tasks;
-	BUG_ON(nr_tasks <= 0);
-
-	ret = ckpt_write_obj_type(ctx, NULL,
-				  sizeof(*h) * nr_tasks,
-				  CKPT_HDR_BUFFER);
-	if (ret < 0)
-		return ret;
-
-	h = ckpt_hdr_get(ctx, sizeof(*h) * CKPT_HDR_PIDS_CHUNK);
-	if (!h)
-		return -ENOMEM;
-
-	do {
-		rcu_read_lock();
-		for (n = 0; n < min(nr_tasks, CKPT_HDR_PIDS_CHUNK); n++) {
-			struct pid_namespace *task_pidns;
-			task = tasks_arr[pos];
-
-			h[n].vpid = task_pid_nr_ns(task, root_pidns);
-			h[n].vtgid = task_tgid_nr_ns(task, root_pidns);
-			h[n].vpgid = task_pgrp_nr_ns(task, root_pidns);
-			h[n].vsid = task_session_nr_ns(task, root_pidns);
-			h[n].vppid = task_tgid_nr_ns(task->real_parent,
-					root_pidns);
-			task_pidns = task_active_pid_ns(task);
-			h[n].depth = task_pidns->level - root_pidns->level;
-
-			ckpt_debug("task[%d]: vpid %d vtgid %d parent %d\n",
-				   pos, h[n].vpid, h[n].vtgid, h[n].vppid);
-			ctx->nr_vpids += h[n].depth;
-			pos++;
-		}
-		rcu_read_unlock();
-
-		n = min(nr_tasks, CKPT_HDR_PIDS_CHUNK);
-		ret = ckpt_kwrite(ctx, h, n * sizeof(*h));
-		if (ret < 0)
-			break;
-
-		nr_tasks -= n;
-	} while (nr_tasks > 0);
-
-	_ckpt_hdr_put(ctx, h, sizeof(*h) * CKPT_HDR_PIDS_CHUNK);
-	return ret;
-}
-
-static int checkpoint_vpids(struct ckpt_ctx *ctx)
-{
-	__s32 *h;  /* vpid array */
-	struct pid_namespace *root_pidns, *task_pidns = NULL, *active_pidns;
-	struct task_struct *task;
-	int ret, nr_tasks = ctx->nr_tasks;
-	int tidx = 0; /* index into task array */
-	int hidx = 0; /* pids written into current __s32 chunk */
-	int vidx = 0; /* vpid index for current task */
-
-	root_pidns = ctx->root_nsproxy->pid_ns;
-	nr_tasks = ctx->nr_tasks;
-
-	ret = ckpt_write_obj_type(ctx, NULL,
-				  sizeof(*h) * ctx->nr_vpids,
-				  CKPT_HDR_BUFFER);
-	if (ret < 0)
-		return ret;
-
-	h = ckpt_hdr_get(ctx, sizeof(*h) * CKPT_HDR_PIDS_CHUNK);
-	if (!h)
-		return -ENOMEM;
-
-	do {
-		rcu_read_lock();
-		while (tidx < nr_tasks && hidx < CKPT_HDR_PIDS_CHUNK) {
-			int nsdelta;
-
-			task = ctx->tasks_arr[tidx];
-			active_pidns = task_active_pid_ns(task);
-			nsdelta = active_pidns->level - root_pidns->level;
-			if (hidx + nsdelta - vidx > CKPT_HDR_PIDS_CHUNK)
-				/*
-				 * We will release rcu before recording the
-				 * remaining vpids, but neither task nor its
-				 * pid can disappear.
-				 */
-				nsdelta = CKPT_HDR_PIDS_CHUNK - hidx + vidx;
-
-			if (vidx == 0)
-				task_pidns = active_pidns;
-			while (vidx++ < nsdelta) {
-				h[hidx++] = task_pid_nr_ns(task, task_pidns);
-				task_pidns = task_pidns->parent;
-			}
-
-			if (task_pidns == root_pidns) {
-				tidx++;
-				vidx = 0;
-			}
-		}
-		rcu_read_unlock();
-
-		ret = ckpt_kwrite(ctx, h, hidx * sizeof(*h));
-		if (ret < 0)
-			break;
-
-		hidx = 0;
-	} while (tidx < nr_tasks);
-
-	_ckpt_hdr_put(ctx, h, sizeof(*h) * CKPT_HDR_PIDS_CHUNK);
-	return ret;
-}
-
 static int collect_objects(struct ckpt_ctx *ctx)
 {
 	int n, ret = 0;
@@ -546,31 +419,321 @@ static int build_tree(struct ckpt_ctx *ctx)
 	return 0;
 }
 
+static int checkpoint_pids_build(struct ckpt_ctx *ctx,
+				 struct flex_array *pids_arr,
+				 int *nr_pids, int *nr_vpids)
+{
+	struct pid_namespace *root_pidns;
+	struct pid *pid, *tgid, *pgrp, *session;
+	struct pid *root_session;
+	struct task_struct *task;
+	int i = 0, depth = 0;
+	int n, new, ret = 0;
+
+	/* safe because we reference the task */
+	root_session = get_pid(task_session(ctx->root_task));
+	root_pidns = ctx->root_nsproxy->pid_ns;
+
+	for (n = 0; n < ctx->nr_tasks; n++) {
+		task = ctx->tasks_arr[n];
+
+		rcu_read_lock();
+		pid = get_pid(task_pid(task));
+		tgid = get_pid(task_tgid(task));
+		pgrp = get_pid(task_pgrp(task));
+		session = get_pid(task_session(task));
+		rcu_read_unlock();
+
+		/*
+		 * How to handle references to pids outside our pid-ns ?
+		 * In container checkpoint, such pids are prohibited, so
+		 * we report an error.
+		 * In subtree checkpoint it is valid, however, we don't
+		 * collect them here to not leak data (it is irrelevant
+		 * to userspace anyway), Instead, in checkpoint_tree() we
+		 * substitute 0 for the such pgrp/session entries.
+		 */
+
+		/* pid */
+		ret = ckpt_obj_lookup_add(ctx, pid,
+					  CKPT_OBJ_PID, &new);
+		if (ret >= 0 && new) {
+			depth += pid->level - root_pidns->level;
+			ret = flex_array_put(pids_arr, i++, pid, GFP_KERNEL);
+			new = 0;
+		}
+
+		/* tgid: if tgid != pid) */
+		if (ret >= 0 && tgid != pid)
+			ret = ckpt_obj_lookup_add(ctx, tgid,
+						  CKPT_OBJ_PID, &new);
+		if (ret >= 0 && new) {
+			depth += tgid->level - root_pidns->level;
+			ret = flex_array_put(pids_arr, i++, tgid, GFP_KERNEL);
+			new = 0;
+		}
+
+		/*
+		 * pgrp: if in our pid-namespace, and
+		 *       if pgrp != tgid, and if pgrp != root_session
+		 */
+		if (pid_nr_ns(pgrp, root_pidns) == 0) {
+			/* pgrp must be ours in container checkpoint */
+			if (!(ctx->uflags & CHECKPOINT_SUBTREE))
+				ret = -EBUSY;
+		} else if (ret >= 0 && pgrp != tgid && pgrp != root_session)
+			ret = ckpt_obj_lookup_add(ctx, pgrp,
+						  CKPT_OBJ_PID, &new);
+		if (ret >= 0 && new) {
+			depth += pgrp->level - root_pidns->level;
+			ret = flex_array_put(pids_arr, i++, pgrp, GFP_KERNEL);
+			new = 0;
+		}
+
+		/*
+		 * session: if in our pid-namespace, and
+		 *          if session != tgid, and if session != root_session
+		 */
+		if (pid_nr_ns(session, root_pidns) == 0) {
+			/* session must be ours in container checkpoint */
+			if (!(ctx->uflags & CHECKPOINT_SUBTREE))
+				ret = -EBUSY;
+		} else if (ret >= 0 && session != tgid && session != root_session)
+			ret = ckpt_obj_lookup_add(ctx, session,
+						  CKPT_OBJ_PID, &new);
+		if (ret >= 0 && new) {
+			depth += session->level - root_pidns->level;
+			ret = flex_array_put(pids_arr, i++, session, GFP_KERNEL);
+		}
+
+		put_pid(pid);
+		put_pid(tgid);
+		put_pid(pgrp);
+		put_pid(session);
+
+		if (ret < 0)
+			break;
+	}
+
+	*nr_pids = i;
+	*nr_vpids = depth;
+
+	ckpt_debug("nr_pids = %d, nr_vpids = %d\n", i, depth);
+	return ret;
+}
+
+static int checkpoint_pids_dump(struct ckpt_ctx *ctx,
+				struct flex_array *pids_arr,
+				int nr_pids, int nr_vpids)
+{
+	struct ckpt_hdr_pids *hh;
+	struct ckpt_pids *h;
+	struct pid *pid;
+	char *buf;
+	int root_level;
+	int len, pos;
+	int depth = 0;
+	int i, n = 0;
+	int ret;
+
+	hh = ckpt_hdr_get_type(ctx, sizeof(*hh), CKPT_HDR_PIDS);
+	if (!hh)
+		return -ENOMEM;
+
+	hh->nr_pids = nr_pids;
+	hh->nr_vpids = nr_vpids;
+
+	ret = ckpt_write_obj(ctx, &hh->h);
+	ckpt_hdr_put(ctx, hh);
+	if (ret < 0)
+		return ret;
+
+	pos = (nr_pids * sizeof(*h)) + (nr_vpids * sizeof(__s32));
+	ret = ckpt_write_obj_type(ctx, NULL, pos, CKPT_HDR_BUFFER);
+	if (ret < 0)
+		return ret;
+
+	buf = ckpt_hdr_get(ctx, PAGE_SIZE);
+	if (!buf)
+		return -ENOMEM;
+
+	root_level = ctx->root_nsproxy->pid_ns->level;
+
+	while (n < nr_pids) {
+		pos = 0;
+
+		rcu_read_lock();
+		while (1) {
+			pid = flex_array_get(pids_arr, n);
+			len = sizeof(*h) + pid->level * sizeof(__s32);
+
+			/* need to flush current buffer ? */
+			if (pos + len > PAGE_SIZE || n == nr_pids)
+				break;
+
+			h = (struct ckpt_pids *) &buf[pos];
+			h->depth = pid->level - root_level;
+			for (i = 0; i <= h->depth; i++)
+				h->numbers[i] = pid->numbers[pid->level + i].nr;
+			depth += h->depth;
+			pos += len;
+			n++;
+		}
+		rcu_read_unlock();
+
+		/* something must have changed since last count... */
+		if (depth > nr_vpids) {
+			ret = -EBUSY;
+			break;
+		}
+
+		ret = ckpt_kwrite(ctx, buf, pos);
+		if (ret < 0)
+			break;
+	}
+
+	_ckpt_hdr_put(ctx, buf, PAGE_SIZE);
+	return ret;
+}
+
+/* dump the array of all pids encountered so far */
+static int checkpoint_pids(struct ckpt_ctx *ctx)
+{
+	struct flex_array *pids_arr;
+	int nr_vpids = 0;
+	int nr_pids = 0;
+	int ret;
+
+	pids_arr = flex_array_alloc(sizeof(struct pid),
+				    4 * ctx->nr_tasks,
+				    GFP_KERNEL);
+	if (!pids_arr)
+		return -ENOMEM;
+
+	ret = checkpoint_pids_build(ctx, pids_arr, &nr_pids, &nr_vpids);
+	if (ret >= 0)
+		ret = checkpoint_pids_dump(ctx, pids_arr, nr_pids, nr_vpids);
+
+	flex_array_free(pids_arr);
+	return ret;
+}
+
+int ckpt_lookup_pid(struct ckpt_ctx *ctx, struct pid *pid)
+{
+	int objref;
+
+	if (!pid)
+		return CKPT_PID_NULL;
+
+	objref = ckpt_obj_lookup(ctx, pid, CKPT_OBJ_PID);
+	if (objref < 0) {
+		objref = 0;  /* outside namespace */
+		WARN(ckpt_pid_vnr(ctx, pid),
+		     "unrecognized pid %d (vnr: %d)\n",
+		     pid->numbers[0].nr, pid_vnr(pid));
+	}
+
+	return objref;
+}
+
 /* dump the array that describes the tasks tree */
 static int checkpoint_tree(struct ckpt_ctx *ctx)
 {
-	struct ckpt_hdr_tree *h;
+	struct pid_namespace *root_pidns;
+	struct pid_namespace *task_pidns;
+	struct task_struct *task, *pp;
+	struct ckpt_hdr_tree *hh;
+	struct ckpt_task_pids *h;
+	int pos, n = 0;
 	int ret;
 
-	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TREE);
-	if (!h)
+	hh = ckpt_hdr_get_type(ctx, sizeof(*hh), CKPT_HDR_TREE);
+	if (!hh)
 		return -ENOMEM;
 
-	h->nr_tasks = ctx->nr_tasks;
+	hh->nr_tasks = ctx->nr_tasks;
 
-	ret = ckpt_write_obj(ctx, &h->h);
-	ckpt_hdr_put(ctx, h);
+	ret = ckpt_write_obj(ctx, &hh->h);
+	ckpt_hdr_put(ctx, hh);
 	if (ret < 0)
 		return ret;
 
-	ret = checkpoint_pids(ctx);
+	pos = ctx->nr_tasks * sizeof(*h);
+	ret = ckpt_write_obj_type(ctx, NULL, pos, CKPT_HDR_BUFFER);
 	if (ret < 0)
 		return ret;
 
-	if (ctx->nr_vpids == 0)
-		return 0;
+	h = ckpt_hdr_get(ctx, PAGE_SIZE);
+	if (!h)
+		return -ENOMEM;
+
+	root_pidns = ctx->root_nsproxy->pid_ns;
+
+	/*
+	 * Record the pids, as seen from ctx->root_nsproxy->pidns,
+	 * saving them as pid-object tags. This info is needed at
+	 * restart to unambiguously dereference tasks.
+	 *
+	 * NOTE: if a pgid/sid refers to an ancestor namespace, we
+	 * simply store a "0" for the tag. This allows restart to
+	 * correctly restore such out-of-pidns references. However,
+	 * this means that restart of non-container checkpoint may be
+	 * inaccurate: sid of different tasks may come from different
+	 * out-of-pidns pids originally, but will refer to the same
+	 * one after the restart. (I wonder if that is needed ?)
+	 */
+
+	while (n < ctx->nr_tasks) {
+		pos = 0;
+
+		rcu_read_lock();
+		while (pos < PAGE_SIZE / sizeof(*h) && n < ctx->nr_tasks) {
+			task = ctx->tasks_arr[pos];
+			pp = task->real_parent;
+			task_pidns = task_active_pid_ns(task);
+
+			h[n].vpid = ckpt_obj_lookup(ctx, task_pid(task),
+						    CKPT_OBJ_PID);
+			h[n].vtgid = ckpt_obj_lookup(ctx, task_tgid(task),
+						     CKPT_OBJ_PID);
+
+			h[n].vpgid = ckpt_lookup_pid(ctx, task_pgrp(task));
+			h[n].vsid = ckpt_lookup_pid(ctx, task_session(task));
+			h[n].vppid = ckpt_lookup_pid(ctx, task_pid(pp));
+
+			h[n].depth = task_pidns->level - root_pidns->level;
+
+			ckpt_debug("task[%d]: vpid %d vtgid %d "
+				   "vpgid %d vsid %d parent %d\n",
+				   pos, task_pid_nr_ns(task, root_pidns),
+				   task_tgid_nr_ns(task, root_pidns),
+				   task_pgrp_nr_ns(task, root_pidns),
+				   task_session_nr_ns(task, root_pidns),
+				   task_tgid_nr_ns(pp, root_pidns));
+
+			if (h[n].vpid <= 0 || h[n].vtgid <= 0 ||
+			    h[n].vpgid < 0 || h[n].vsid < 0)
+				break;
+
+			pos++;
+			n++;
+		}
+		rcu_read_unlock();
 
-	return checkpoint_vpids(ctx);
+		/*
+		 * The root task's vppid must be 0 because the parent pid
+		 * was never collected. If that is not the case, something
+		 * went wrong ...
+		 */
+		WARN_ON(n == pos && h[0].vppid != 0);
+
+		ret = ckpt_kwrite(ctx, h, pos * sizeof(*h));
+		if (ret < 0)
+			break;
+	}
+
+	_ckpt_hdr_put(ctx, h, PAGE_SIZE);
+	return ret;
 }
 
 static struct task_struct *get_freezer_task(struct task_struct *root_task)
@@ -715,6 +878,9 @@ long do_checkpoint(struct ckpt_ctx *ctx, pid_t pid)
 	ret = checkpoint_container(ctx);
 	if (ret < 0)
 		goto out;
+	ret = checkpoint_pids(ctx);
+	if (ret < 0)
+		goto out;
 	ret = checkpoint_tree(ctx);
 	if (ret < 0)
 		goto out;
diff --git a/kernel/checkpoint/process.c b/kernel/checkpoint/process.c
index 33bb62d..a39a6d4 100644
--- a/kernel/checkpoint/process.c
+++ b/kernel/checkpoint/process.c
@@ -25,56 +25,6 @@
 #include <linux/checkpoint.h>
 #include <linux/pid_namespace.h>
 
-pid_t ckpt_pid_nr(struct ckpt_ctx *ctx, struct pid *pid)
-{
-	return pid ? pid_nr_ns(pid, ctx->root_nsproxy->pid_ns) : CKPT_PID_NULL;
-}
-
-/* must be called with tasklist_lock or rcu_read_lock() held */
-struct pid *_ckpt_find_pgrp(struct ckpt_ctx *ctx, pid_t pgid)
-{
-	struct task_struct *p;
-	struct pid *pgrp;
-
-	if (pgid == 0) {
-		/*
-		 * At checkpoint the pgid owner lived in an ancestor
-		 * pid-ns. The best we can do (sanely and safely) is
-		 * to examine the parent of this restart's root: if in
-		 * a distinct pid-ns, use its pgrp; otherwise fail.
-		 */
-		p = ctx->root_task->real_parent;
-		if (p->nsproxy->pid_ns == current->nsproxy->pid_ns)
-			return NULL;
-		pgrp = task_pgrp(p);
-	} else {
-		/*
-		 * Find the owner process of this pgid (it must exist
-		 * if pgrp exists). It must be a thread group leader.
-		 */
-		pgrp = find_pid_ns(pgid, ctx->root_nsproxy->pid_ns);
-		p = pid_task(pgrp, PIDTYPE_PID);
-		if (!p || !thread_group_leader(p))
-			return NULL;
-		/*
-		 * The pgrp must "belong" to our restart tree (compare
-		 * p->checkpoint_ctx to ours). This prevents malicious
-		 * input from (guessing and) using unrelated pgrps. If
-		 * the owner is dead, then it doesn't have a context,
-		 * so instead compare against its (real) parent's.
-		 */
-		if (p->exit_state == EXIT_ZOMBIE)
-			p = p->real_parent;
-		if (p->checkpoint_ctx != ctx)
-			return NULL;
-	}
-
-	if (task_session(current) != task_session(p))
-		return NULL;
-
-	return pgrp;
-}
-
 #ifdef CONFIG_FUTEX
 static void save_task_robust_futex_list(struct ckpt_hdr_task *h,
 					struct task_struct *t)
@@ -601,7 +551,7 @@ static int restore_task_ns(struct ckpt_ctx *ctx)
 		goto out;
 	}
 
-	if (nsproxy != task_nsproxy(current)) {
+	if (nsproxy != current->nsproxy) {
 		spin_lock(&checkpoint_nslock);
 		if (!nsproxy->pid_ns)
 			nsproxy->pid_ns = get_pid_ns(current->nsproxy->pid_ns);
@@ -610,7 +560,7 @@ static int restore_task_ns(struct ckpt_ctx *ctx)
 		switch_task_namespaces(current, nsproxy);
 	}
  out:
-	ckpt_debug("nsproxy: ret %d (%p)\n", ret, task_nsproxy(current));
+	ckpt_debug("nsproxy: ret %d (%p)\n", ret, current->nsproxy);
 	ckpt_hdr_put(ctx, h);
 	return ret;
 }
@@ -839,56 +789,6 @@ int restore_restart_block(struct ckpt_ctx *ctx)
 	return ret;
 }
 
-static int restore_task_pgid(struct ckpt_ctx *ctx)
-{
-	struct task_struct *task = current;
-	struct pid *pgrp;
-	pid_t pgid;
-	int ret;
-
-	/*
-	 * We enforce the following restrictions on restoring pgrp:
-	 *  1) Only thread group leaders restore pgrp
-	 *  2) Session leader cannot change own pgrp
-	 *  3) Owner of pgrp must belong to same restart tree
-	 *  4) Must have same session as other tasks in same pgrp
-	 *  5) Change must pass setpgid security callback
-	 *
-	 * TODO - check if we need additional restrictions ?
-	 */
-
-	if (!thread_group_leader(task))  /* (1) */
-		return 0;
-
-	pgid = ctx->pids_arr[ctx->active_pid].vpgid;
-
-	if (pgid == task_pgrp_nr_ns(task, ctx->root_nsproxy->pid_ns))
-		return 0;  /* nothing to do */
-
-	if (task->signal->leader)  /* (2) */
-		return -EINVAL;
-
-	ret = -EINVAL;
-
-	write_lock_irq(&tasklist_lock);
-	pgrp = _ckpt_find_pgrp(ctx, pgid);  /* (3) and (4) */
-	if (pgrp && task_pgrp(task) != pgrp) {
-		ret = security_task_setpgid(task, pgid);  /* (5) */
-		if (!ret)
-			change_pid(task, PIDTYPE_PGID, pgrp);
-	}
-	write_unlock_irq(&tasklist_lock);
-
-	/* self-restart: be tolerant if old pgid isn't found */
-	if (ctx->uflags & RESTART_TASKSELF)
-		ret = 0;
-
-	if (ret < 0)
-		ckpt_err(ctx, ret, "setting pgid\n");
-
-	return ret;
-}
-
 /* prepare the task for restore */
 int pre_restore_task(void)
 {
@@ -934,9 +834,6 @@ int restore_task(struct ckpt_ctx *ctx)
 	if (ret)
 		goto out;
 
-	ret = restore_task_pgid(ctx);
-	if (ret < 0)
-		goto out;
 	ret = restore_thread(ctx);
 	ckpt_debug("thread %d\n", ret);
 	if (ret < 0)
@@ -949,6 +846,7 @@ int restore_task(struct ckpt_ctx *ctx)
 	ckpt_debug("cpu %d\n", ret);
 	if (ret < 0)
 		goto out;
+
 	ret = restore_task_objs(ctx);
 	ckpt_debug("objs %d\n", ret);
 	if (ret < 0)
diff --git a/kernel/checkpoint/restart.c b/kernel/checkpoint/restart.c
index adcfb23..b3ee00d 100644
--- a/kernel/checkpoint/restart.c
+++ b/kernel/checkpoint/restart.c
@@ -143,12 +143,16 @@ void restore_debug_free(struct ckpt_ctx *ctx)
 	ckpt_debug("%d tasks registered, nr_tasks was %d nr_total %d\n",
 		   count, ctx->nr_tasks, atomic_read(&ctx->nr_total));
 
-	ckpt_debug("active pid was %d, ctx->errno %d\n", ctx->active_pid,
+	ckpt_debug("active pid was %d, ctx->errno %d\n", ctx->active_task,
 		   ctx->errno);
 	ckpt_debug("kflags %lu uflags %lu oflags %lu", ctx->kflags,
 		   ctx->uflags, ctx->oflags);
-	for (i = 0; i < ctx->nr_pids; i++)
-		ckpt_debug("task[%d] to run %d\n", i, ctx->pids_arr[i].vpid);
+	for (i = 0; i < ctx->nr_tasks; i++) {
+		if (!ctx->tasks_arr[i])
+			continue;
+		ckpt_debug("task[%d] to run %d\n", i,
+			   ckpt_task_vnr(ctx, ctx->tasks_arr[i]));
+	}
 
 	list_for_each_entry_safe(s, p, &ctx->task_status, list) {
 		if (s->flags & RESTART_DBG_COORD)
@@ -733,73 +737,428 @@ static int restore_read_tail(struct ckpt_ctx *ctx)
 	return ret;
 }
 
-/* restore_read_tree - read the tasks tree into the checkpoint context */
-static int restore_read_tree(struct ckpt_ctx *ctx)
+static struct pid *restore_validate_pids(struct ckpt_ctx *ctx,
+					 struct ckpt_pids *h)
 {
-	struct ckpt_hdr_tree *h;
-	int size, ret;
-
-	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TREE);
-	if (IS_ERR(h))
-		return PTR_ERR(h);
+	struct task_struct *task;
+	struct pid *pid, *pidret = NULL;
+	int i, j;
 
-	ret = -EINVAL;
-	if (h->nr_tasks <= 0)
+	rcu_read_lock();
+	task = find_task_by_pid_ns(h->numbers[0], ctx->root_nsproxy->pid_ns);
+	if (!task || task->checkpoint_ctx != ctx)
 		goto out;
-
-	ctx->nr_pids = h->nr_tasks;
-	size = sizeof(*ctx->pids_arr) * ctx->nr_pids;
-	if (size <= 0)		/* overflow ? */
+	pid = task_pid(task);
+	if (pid->level - task_pid(current)->level != h->depth)
 		goto out;
+	for (i = 0, j = pid->level - h->depth; i <= h->depth; i++, j++)
+		if (pid->numbers[j].nr != h->numbers[i])
+			goto out;
+	pidret = get_pid(pid);
+ out:
+	rcu_read_unlock();
+	return pidret;
+}
 
-	ctx->pids_arr = kmalloc(size, GFP_KERNEL);
-	if (!ctx->pids_arr) {
-		ret = -ENOMEM;
-		goto out;
+/* restore_read_pids - read the pids and validate against new tree */
+static int restore_read_pids(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_pids *hh;
+	struct ckpt_pids *h;
+	struct pid *pid;
+	char *buf = NULL;
+	int p = 0, n = 0, s = 0;
+	int nr_pids, nr_vpids;
+	int len, tot, ret;
+	int depth = 0;
+
+	hh = ckpt_read_obj_type(ctx, sizeof(*hh), CKPT_HDR_PIDS);
+	if (IS_ERR(hh))
+		return PTR_ERR(hh);
+	nr_pids = hh->nr_pids;
+	nr_vpids = hh->nr_vpids;
+	ckpt_hdr_put(ctx, hh);
+
+	if (nr_pids == 0)
+		return -EINVAL;
+
+	tot = nr_pids * sizeof(*h) + nr_vpids * sizeof(__s32);
+	if (tot <= 0)   /* overflow ? */
+		return -EINVAL;
+
+	ret = _ckpt_read_obj_type(ctx, NULL, tot, CKPT_HDR_BUFFER);
+	if (ret < 0)
+		return ret;
+
+	buf = ckpt_hdr_get(ctx, PAGE_SIZE);
+	if (!buf)
+		return -ENOMEM;
+
+	while (n < nr_pids && s < tot) {
+		len = min(tot, (int) PAGE_SIZE - p);
+		ret = ckpt_kread(ctx, buf + p, len);
+		if (ret < 0)
+			break;
+
+		p = 0;
+
+		ret = -EINVAL;
+		while (n < nr_pids && len > 0) {
+			s = sizeof(*h);
+			if (s > len)
+				break;
+
+			h = (struct ckpt_pids *) &buf[p];
+			if (h->depth < 0)
+				goto out;
+
+			s += h->depth * sizeof(__s32);
+			if (s < 0)  /* overflow */
+				goto out;
+			if (s > len)
+				break;
+
+			pid = restore_validate_pids(ctx, h);
+			if (!pid)
+				goto out;
+
+			ret = ckpt_obj_insert(ctx, pid, n + 1, CKPT_OBJ_PID);
+			put_pid(pid);
+			if (ret < 0)
+				goto out;
+
+			depth += h->depth;
+			if (depth > nr_vpids)
+				goto out;
+
+			len -= s;
+			p += s;
+			n++;
+		}
+
+		memcpy(buf, buf + p, len);
+		tot -= len - p;
 	}
-	ret = _ckpt_read_buffer(ctx, ctx->pids_arr, size);
+
+	if (n == nr_pids && tot == 0)
+		ret = 0;
  out:
-	ckpt_hdr_put(ctx, h);
+	_ckpt_hdr_put(ctx, buf, PAGE_SIZE);
 	return ret;
 }
 
-/*
- * read all the vpids - we don't actually care about them,
- * userspace did
- */
-static int restore_slurp_vpids(struct ckpt_ctx *ctx)
+static int restore_task_pgrp(struct ckpt_ctx *ctx,
+			     struct task_struct *task,
+			     struct pid *pgrp)
 {
-	int size, ret, i;
+	struct task_struct *p;
+	pid_t pgid;
+	int ret;
 
-	for (i = 0; i < ctx->nr_pids; i++)
-		ctx->nr_vpids += ctx->pids_arr[i].depth;
+	/*
+	 * We enforce the following restrictions on restoring pgrp:
+	 *  1) Only thread group leaders restore pgrp
+	 *  2) Session leader cannot change own pgrp
+	 *  3) Must have same session as other tasks in same pgrp
+	 *  4) Change must pass setpgid security callback
+	 *
+	 * By now we know that the pgrp belongs to our restart tree,
+	 * because we checked then in restore_validate_pids().
+	 *
+	 * TODO - check if we need additional restrictions ?
+	 */
 
-	if (ctx->nr_vpids == 0)
+	if (!thread_group_leader(task))  /* (1) */
 		return 0;
 
-	size = sizeof(__s32) * ctx->nr_vpids;
-	if (size < 0)		/* overflow ? */
+	if (task->signal->leader)  /* (2) */
+		return -EINVAL;
+
+	ret = -EINVAL;
+	write_lock_irq(&tasklist_lock);
+	if (pgrp == NULL) {
+		/*
+		 * At checkpoint the pgid owner lived in an ancestor
+		 * pid-ns. The best we can do (sanely and safely) is
+		 * to examine the parent of this restart's root: if in
+		 * a distinct pid-ns, use its pgrp; otherwise fail.
+		 */
+		p = ctx->root_task->real_parent;
+		if (p->nsproxy->pid_ns == current->nsproxy->pid_ns)
+			goto unlock;
+	} else {
+		/* Find the owner process - must be a thread leader */
+		p = pid_task(pgrp, PIDTYPE_PID);
+		if (!thread_group_leader(p))
+			goto unlock;
+		/*
+		 * If the owner is dead, then it has no context, so
+		 * instead compare against its (real) parent's.
+		 */
+		if (p->exit_state == EXIT_ZOMBIE)
+			p = p->real_parent;
+		if (p->checkpoint_ctx != ctx)
+			goto unlock;
+	}
+
+	if (task_session(task) != task_session(p))  /* (3) */
+		goto unlock;
+
+	if (task_pgrp(task) != pgrp) {
+		pgid = pid_vnr(pgrp);
+		ret = security_task_setpgid(task, pgid);  /* (4) */
+		if (!ret)
+			change_pid(task, PIDTYPE_PGID, pgrp);
+	} else {
+		/*
+		 * Weird!! We wouldn't be called in this case!!
+		 * Anyway, the pgrp is now ok, so silently ignore
+		 */
+		WARN(1, "pgid changed while restore\n");
+		ret = 0;
+	}
+
+ unlock:
+	write_unlock_irq(&tasklist_lock);
+
+	/* self-restart: be tolerant if old pgid isn't found */
+	if (ctx->uflags & RESTART_TASKSELF)
+		ret = 0;
+
+	if (ret < 0)
+		ckpt_err(ctx, ret, "restore pgid\n");
+
+	return ret;
+}
+
+static struct task_struct *restore_validate_task(struct ckpt_ctx *ctx,
+						 struct ckpt_task_pids *h)
+{
+	struct task_struct *task;
+	struct pid_namespace *root_pidns;
+	struct pid *pid, *tgid;
+	struct pid *pgrp = NULL;
+	struct pid *session = NULL;
+	int ret = 0;
+
+	pid = ckpt_obj_fetch(ctx, h->vpid, CKPT_OBJ_PID);
+	tgid = ckpt_obj_fetch(ctx, h->vtgid, CKPT_OBJ_PID);
+
+	if (h->vpgid != 0 && h->vpgid != CKPT_PID_ROOT)
+		pgrp = ckpt_obj_fetch(ctx, h->vpgid, CKPT_OBJ_PID);
+	if (h->vsid != 0 && h->vsid != CKPT_PID_ROOT)
+		session = ckpt_obj_fetch(ctx, h->vsid, CKPT_OBJ_PID);
+	if (IS_ERR(pid))
+		return ERR_CAST(pid);
+	if (IS_ERR(tgid))
+		return ERR_CAST(tgid);
+	if (IS_ERR(pgrp))
+		return ERR_CAST(pgrp);
+	if (IS_ERR(session))
+		return ERR_CAST(session);
+
+	rcu_read_lock();
+	read_lock(&tasklist_lock);
+
+	task = pid_task(pid, PIDTYPE_PID);  /* get the owner */
+	root_pidns = ctx->root_nsproxy->pid_ns;
+
+	/*
+	 * If vpgid/vsid is 0, then at checkpoint time it was a
+	 * reference to a pid from an ancestor pid-ns, inherited
+	 * through the root task. For vsid, verify that this is the
+	 * case now. For pgid, verify that the coordinator (or its
+	 * parent) is in ancestor pis-ns, and use their pid.
+	 *
+	 * NOTE: this means that restart of non-container checkpoint
+	 * may be inaccurate: sid of different tasks may come from
+	 * different out-of-pidns pids originally, but will refer to
+	 * the same one after the restart. Don't think it's useful.
+	 *
+	 * If vpgid/vsid is CKPT_PID_ROOT, then at checkpoint time it
+	 * was the same as the root task's sid, and the root task was
+	 * not a session leader (otherwise, they would be 1). We now
+	 * verify that the restarted root task isn't a session leader
+	 * and substitue its sid for the vpgid/vsid in question.
+	 */
+
+	if (!session) {
+		if (h->vsid == CKPT_PID_ROOT &&
+		    !ctx->root_task->signal->leader &&
+		    task_session(task) == task_session(ctx->root_task)) {
+			/* must have same sid as root task */
+			session = task_session(ctx->root_task);
+		} else if (h->vsid == 0 &&
+			   pid_nr_ns(task_session(task), root_pidns) == 0) {
+			/*  must be in different pid-ns */
+			session = task_session(task);
+		}
+	}
+
+	if (!pgrp) {
+		if (h->vpgid == CKPT_PID_ROOT &&
+		    !ctx->root_task->signal->leader &&
+		    task_pgrp(task) == task_session(ctx->root_task)) {
+			/* must have same sid as root task */
+			pgrp = task_session(ctx->root_task);
+		} else if (h->vsid == 0) {
+			struct task_struct *t = current;
+			/*  must be in different pid-ns - try to grab
+			    the session of coord's or coord's parent */
+			if (pid_nr_ns(task_pgrp(t), root_pidns) != 0)
+				t = rcu_dereference(current->real_parent);
+			if (pid_nr_ns(task_pgrp(t), root_pidns) == 0)
+				pgrp = task_pgrp(t);
+		} else
+			pgrp = ERR_PTR(-EINVAL);
+	}
+
+	/*
+	 * Verify that the task matches our expectations in terms of:
+	 * checkpoint context, tgid, session, and pidns depth. Don't
+	 * enforce pgrp as it may not match (restored below)
+	 */
+
+	if (!IS_ERR(task) && task->checkpoint_ctx == ctx &&
+	    tgid == task_tgid(task) && session == task_session(task) &&
+	    h->depth == task_active_pid_ns(task)->level - root_pidns->level) {
+		/* yes, this is our task ! */
+		get_task_struct(task);
+	} else {
+		task = ERR_PTR(-EINVAL);
+	}
+
+	rcu_read_unlock();
+	read_unlock(&tasklist_lock);
+
+	if (IS_ERR(task))
+		return task;
+
+	/*
+	 * The pgrp may not match the task's pgrp (the restarted tree
+	 * does not guarantee this), or could be NULL e.g., if we are
+	 * restartign from a subtree. Call restore_task_pgrp() to fix.
+	 */
+	if (pgrp != task_pgrp(task)) {
+		ret = restore_task_pgrp(ctx, task, pgrp);
+		if (ret < 0) {
+			put_task_struct(task);
+			task = ERR_PTR(ret);
+		}
+	}
+
+	return task;
+}
+
+/* restore_read_tree - read the tasks tree into the checkpoint context */
+static int restore_read_tree(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_tree *hh;
+	struct ckpt_task_pids *h;
+	struct task_struct *task;
+	int nr_tasks;
+	int len, ret;
+	int p, n = 0;
+
+	hh = ckpt_read_obj_type(ctx, sizeof(*hh), CKPT_HDR_TREE);
+	if (IS_ERR(hh))
+		return PTR_ERR(hh);
+	nr_tasks = hh->nr_tasks;
+	ckpt_hdr_put(ctx, hh);
+
+	if (nr_tasks <= 0)
+		return -EINVAL;
+
+	len = sizeof(*h) * nr_tasks;
+	if (len <= 0)		/* overflow ? */
 		return -EINVAL;
 
-	ret = ckpt_read_consume(ctx, size + sizeof(struct ckpt_hdr),
-				CKPT_HDR_BUFFER);
+	ret = _ckpt_read_obj_type(ctx, NULL, len, CKPT_HDR_BUFFER);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Actual tasks count may exceed ctx->nr_tasks due of 'dead'
+	 * tasks used as place-holders for PGIDs, but not fall short.
+	 */
+	if (atomic_read(&ctx->nr_total) < nr_tasks)
+		return -ESRCH;
+
+	/* last entry intentionally remains NULL: see get_active_task() */
+	ctx->nr_tasks = nr_tasks;
+	ctx->tasks_arr = kzalloc(len + 1, GFP_KERNEL);
+	if (!ctx->tasks_arr)
+		return -ENOMEM;
+
+	h = ckpt_hdr_get(ctx, PAGE_SIZE);
+	if (!h) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	while (n < nr_tasks) {
+		len = min((int)(PAGE_SIZE / sizeof(*h)), nr_tasks - n);
+		ret = ckpt_kread(ctx, h, len * sizeof(*h));
+		if (ret < 0)
+			break;
+
+		p = 0;
+
+		ret = -EINVAL;
+		while (n < nr_tasks && p < len) {
+			task = restore_validate_task(ctx, &h[p]);
+			if (IS_ERR(task)) {
+				ret = PTR_ERR(task);
+				goto out;
+			}
+			ctx->tasks_arr[n] = task;
+			p++;
+			n++;
+		}
+	}
+
+	if (n == nr_tasks)
+		ret = 0;
+
+#ifdef CONFIG_CHECKPOINT_DEBUG
+	ckpt_debug("restoring tasks......\n");
+	for (n = 0; n < nr_tasks; n++)
+		ckpt_debug("task[%d]: pid %d (%d)\n", n,
+			   task_pid_vnr(ctx->tasks_arr[n]),
+			   task_pid_nr_ns(ctx->tasks_arr[n],
+					  ctx->root_nsproxy->pid_ns));
+	ckpt_debug(".....................\n");
+#endif
+
+ out:
+	_ckpt_hdr_put(ctx, h, PAGE_SIZE);
 	return ret;
 }
 
 static inline int all_tasks_activated(struct ckpt_ctx *ctx)
 {
-	return (ctx->active_pid == ctx->nr_pids);
+	return (ctx->active_task == ctx->nr_tasks);
 }
 
-static inline pid_t get_active_pid(struct ckpt_ctx *ctx)
+static inline struct task_struct *get_active_task(struct ckpt_ctx *ctx)
 {
-	int active = ctx->active_pid;
-	return active >= 0 ? ctx->pids_arr[active].vpid : 0;
+	int active = ctx->active_task;
+
+	/*
+	 * This is safe even for (active == ctx->nr)_tasks because the
+	 * ctx->tasks_arr[] array has an extra (NULL) slot at the end,
+	 * This may happen if due to bad input a restarting task is
+	 * not in the ctx->tasks_arr, but calls wait_task_active().
+	 * It may then wake up and call us with active_task already
+	 * maxed out...
+	 */
+	BUG_ON(active > ctx->nr_tasks);
+	return active >= 0 ? ctx->tasks_arr[active] : NULL;
 }
 
-static inline int is_task_active(struct ckpt_ctx *ctx, pid_t pid)
+static inline int is_task_active(struct ckpt_ctx *ctx, struct task_struct *task)
 {
-	return get_active_pid(ctx) == pid;
+	return get_active_task(ctx) == task;
 }
 
 /*
@@ -862,31 +1221,13 @@ static void restore_task_done(struct ckpt_ctx *ctx)
 
 static int restore_activate_next(struct ckpt_ctx *ctx)
 {
-	struct task_struct *task;
-	pid_t pid;
-
-	ctx->active_pid++;
+	ctx->active_task++;
 
-	BUG_ON(ctx->active_pid > ctx->nr_pids);
+	BUG_ON(ctx->active_task > ctx->nr_tasks);
 
 	if (!all_tasks_activated(ctx)) {
 		/* wake up next task in line to restore its state */
-		pid = get_active_pid(ctx);
-
-		rcu_read_lock();
-		task = find_task_by_pid_ns(pid,
-					task_active_pid_ns(ctx->root_task));
-		/* target task must have same restart context */
-		if (task && task->checkpoint_ctx == ctx)
-			wake_up_process(task);
-		else
-			task = NULL;
-		rcu_read_unlock();
-
-		if (!task) {
-			ckpt_err(ctx, -ESRCH, "task %d not found\n", pid);
-			return -ESRCH;
-		}
+		wake_up_process(get_active_task(ctx));
 	} else {
 		/* wake up ghosts tasks so that they can terminate */
 		wake_up_all(&ctx->ghostq);
@@ -897,15 +1238,14 @@ static int restore_activate_next(struct ckpt_ctx *ctx)
 
 static int wait_task_active(struct ckpt_ctx *ctx)
 {
-	pid_t pid = task_pid_nr_ns(current, task_active_pid_ns(ctx->root_task));
 	int ret;
 
-	ckpt_debug("pid %d waiting\n", pid);
+	ckpt_debug("pid %d waiting\n", ckpt_task_vnr(ctx, current));
 	ret = wait_event_interruptible(ctx->waitq,
-				       is_task_active(ctx, pid) ||
+				       is_task_active(ctx, current) ||
 				       ckpt_test_error(ctx));
 	ckpt_debug("active %d < %d (ret %d, errno %d)\n",
-		   ctx->active_pid, ctx->nr_pids, ret, ctx->errno);
+		   ctx->active_task, ctx->nr_tasks, ret, ctx->errno);
 	if (ckpt_test_error(ctx))
 		return ckpt_get_error(ctx);
 	return 0;
@@ -1140,29 +1480,22 @@ static int __prepare_descendants(struct task_struct *task, void *data)
  */
 static int prepare_descendants(struct ckpt_ctx *ctx, struct task_struct *root)
 {
-	int nr_pids;
+	int nr_total;
 
-	nr_pids = walk_task_subtree(root, __prepare_descendants, ctx);
-	ckpt_debug("nr %d/%d\n", ctx->nr_pids, nr_pids);
-	if (nr_pids < 0)
-		return nr_pids;
+	nr_total = walk_task_subtree(root, __prepare_descendants, ctx);
+	ckpt_debug("nr %d/%d\n", ctx->nr_tasks, nr_total);
+	if (nr_total < 0)
+		return nr_total;
 
-	/*
-	 * Actual tasks count may exceed ctx->nr_pids due of 'dead'
-	 * tasks used as place-holders for PGIDs, but not fall short.
-	 */
-	if (nr_pids < ctx->nr_pids)
-		return -ESRCH;
-
-	atomic_set(&ctx->nr_total, nr_pids);
-	return nr_pids;
+	atomic_set(&ctx->nr_total, nr_total);
+	return nr_total;
 }
 
 static int wait_all_tasks_finish(struct ckpt_ctx *ctx)
 {
 	int ret;
 
-	BUG_ON(ctx->active_pid != -1);
+	BUG_ON(ctx->active_task != -1);
 	ret = restore_activate_next(ctx);
 	if (ret < 0)
 		return ret;
@@ -1206,6 +1539,8 @@ static int init_restart_ctx(struct ckpt_ctx *ctx, pid_t pid)
 	 * occurs then ckpt_ctx_free() is eventually called.
 	 */
 
+	ckpt_debug("restore context: root pid %d\n", pid);
+
 	if (!choose_root_task(ctx, pid))
 		return -ESRCH;
 
@@ -1219,7 +1554,7 @@ static int init_restart_ctx(struct ckpt_ctx *ctx, pid_t pid)
 	if (!nsproxy)
 		return -ESRCH;
 
-	ctx->active_pid = -1;	/* see restore_activate_next, get_active_pid */
+	ctx->active_task = -1;	/* see restore_activate_next, get_active_task */
 
 	return 0;
 }
@@ -1246,8 +1581,13 @@ static int do_restore_coord(struct ckpt_ctx *ctx, pid_t pid)
 	ret = restore_debug_task(ctx, RESTART_DBG_COORD);
 	if (ret < 0)
 		return ret;
+
 	restore_debug_running(ctx);
 
+	ret = init_restart_ctx(ctx, pid);
+	if (ret < 0)
+		return ret;
+
 	ret = restore_read_header(ctx);
 	ckpt_debug("restore header: %d\n", ret);
 	if (ret < 0)
@@ -1256,22 +1596,6 @@ static int do_restore_coord(struct ckpt_ctx *ctx, pid_t pid)
 	ckpt_debug("restore container: %d\n", ret);
 	if (ret < 0)
 		return ret;
-	ret = restore_read_tree(ctx);
-	ckpt_debug("restore tree: %d\n", ret);
-	if (ret < 0)
-		return ret;
-
-	ret = restore_slurp_vpids(ctx);
-	ckpt_debug("read vpids %d\n", ret);
-	if (ret < 0)
-		return ret;
-
-	if ((ctx->uflags & RESTART_TASKSELF) && ctx->nr_pids != 1)
-		return -EINVAL;
-
-	ret = init_restart_ctx(ctx, pid);
-	if (ret < 0)
-		return ret;
 
 	/*
 	 * Populate own ->checkpoint_ctx: if an ancestor attempts to
@@ -1284,7 +1608,7 @@ static int do_restore_coord(struct ckpt_ctx *ctx, pid_t pid)
 		 * We are a bad-behaving descendant: an ancestor must
 		 * have prepare_descendants() us as part of a restart.
 		 */
-		ckpt_debug("coord already has checkpoint_ctx\n");
+		ckpt_debug("coord/self already has checkpoint_ctx\n");
 		return -EBUSY;
 	}
 
@@ -1294,6 +1618,26 @@ static int do_restore_coord(struct ckpt_ctx *ctx, pid_t pid)
 	 * subtree that we marked for restart - see below.
 	 */
 
+	if (!(ctx->uflags & RESTART_TASKSELF)) {
+		/* prepare descendants' t->checkpoint_ctx point to coord */
+		ret = prepare_descendants(ctx, ctx->root_task);
+		ckpt_debug("restore prepare: %d\n", ret);
+		if (ret < 0)
+			goto out;
+	}
+
+	ret = restore_read_pids(ctx);
+	ckpt_debug("restore pids: %d\n", ret);
+	if (ret < 0)
+		goto out;
+	ret = restore_read_tree(ctx);
+	ckpt_debug("restore tree: %d\n", ret);
+	if (ret < 0)
+		goto out;
+
+	if ((ctx->uflags & RESTART_TASKSELF) && ctx->nr_tasks != 1)
+		return -EINVAL;
+
 	if (ctx->uflags & RESTART_TASKSELF) {
 		ret = pre_restore_task();
 		ckpt_debug("pre restore task: %d\n", ret);
@@ -1304,11 +1648,6 @@ static int do_restore_coord(struct ckpt_ctx *ctx, pid_t pid)
 		if (ret < 0)
 			goto out;
 	} else {
-		/* prepare descendants' t->checkpoint_ctx point to coord */
-		ret = prepare_descendants(ctx, ctx->root_task);
-		ckpt_debug("restore prepare: %d\n", ret);
-		if (ret < 0)
-			goto out;
 		/* wait for all other tasks to complete do_restore_task() */
 		ret = wait_all_tasks_finish(ctx);
 		ckpt_debug("restore finish: %d\n", ret);
@@ -1454,7 +1793,7 @@ void exit_checkpoint(struct task_struct *tsk)
 
 	/* restarting zombies will activate next task in restart */
 	if (tsk->flags & PF_RESTARTING) {
-		BUG_ON(ctx->active_pid == -1);
+		BUG_ON(ctx->active_task == -1);
 		restore_task_done(ctx);
 	}
 
diff --git a/kernel/checkpoint/sys.c b/kernel/checkpoint/sys.c
index e9a377b..36a0c6e 100644
--- a/kernel/checkpoint/sys.c
+++ b/kernel/checkpoint/sys.c
@@ -241,8 +241,6 @@ static void ckpt_ctx_free(struct ckpt_ctx *ctx)
 	if (ctx->tasks_arr)
 		task_arr_free(ctx);
 
-	if (ctx->coord_pidns)
-		put_pid_ns(ctx->coord_pidns);
 	if (ctx->root_nsproxy)
 		put_nsproxy(ctx->root_nsproxy);
 	if (ctx->root_task)
@@ -252,8 +250,6 @@ static void ckpt_ctx_free(struct ckpt_ctx *ctx)
 
 	free_page((unsigned long) ctx->scratch_page);
 
-	kfree(ctx->pids_arr);
-
 #ifdef CONFIG_NETNS_CHECKPOINT
 	sock_listening_list_free(&ctx->listen_sockets);
 #endif
@@ -274,7 +270,6 @@ static struct ckpt_ctx *ckpt_ctx_alloc(int fd, unsigned long uflags,
 	ctx->uflags = uflags;
 	ctx->kflags = kflags;
 	ctx->ktime_begin = ktime_get();
-	ctx->coord_pidns = get_pid_ns(current->nsproxy->pid_ns);
 
 	atomic_set(&ctx->refcount, 0);
 	INIT_LIST_HEAD(&ctx->pgarr_list);
-- 
1.7.1

Re: [PATCH 4/5] c/r: checkpoint and restart pids objects

[Sukadev Bhattiprolu]

Oren:

I am still reviewing this patchset, but have a few questions/comments
below on this patch.

| From: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
| Subject: [PATCH 4/5] c/r: checkpoint and restart pids objects
| 
| Make use of (shared) pids objects instead of simply saving the pid_t
| numbers in both checkpoint and restart.
| 
| The motivation for this change is twofold. First, since pid-ns came to
| life pid's in the kenrel _are_ shared objects and should be treated as
| such. This is useful e.g. for tty handling and also file-ownership
| (the latter waiting for this feature). Second, to properly support
| nested namesapces we need to report with each pid the entire list of
| pid numbers, not only a single pid. While current we do that for all
| "live" pids (those that belong to live tasks), we didn't do it for
| "dead" pids (to be assigned to ghost restarting tasks).
| 
| Note, that ideally the list of vpids of a pid object should also
| include the pid-ns to which each level belongs; however, in this patch
| we don't yet hanlde that. So only linear pid-nesting works well and
| not arbitrary tree.
| 
| DICLAIMER: this patch is big and intrusive!  Here is a summary of the
| changes that it makes:
| 
| CHECKPOINT:
| 
| 1) Modified the data structures used to describe pids and tasks' pids:
|  struct ckpt_pids - for the data of a pids object (depth, numbers)
|    (pids objects are collected in the order found, and are assigned
|    tags sequentially, starting from 1)
|  struct ckpt_task_pids - for a task's pids, holding the _tag_ of the
|    corresponding pids object rather than their pid numbers themselves.
| 
| 2) Accordingly, two arrays are used to hold this information:
|  ctx->pids_arr - array of 'struct ckpt_pids' collected from the tasks
|    and the pids they reference. Entries are of variable size depending
|    on the pid-ns nesting level.
|  ctx->tasks_arr - array of 'struct ckpt_task_pids' collected from teh
|    tasks. Entries are of fixed size, and hold the objref tags to the
|  shared pids objects rather than actual pid numbers.
|  (the old vpids_arr is no longer needed, nor written separately).
| 
| 3) We now first write the pids information, then tasks' pids.
| 
| 4) checkpoint_pids() builds and writes the ctx->pids_arr:
|  checkpoint_pids_build() - iterates over the tasks and collects the
|    unique pids in a flex_array (also inserts them into the objhash)
|  checkpoint_pids_dumps() - dumps the data from the flex_array in
|    the format of ctx->tasks_arr
| 
| 5) checkpoint_tree() dumps the tasks' pids information, by scanning
|  all the tasks and writing out tags of the pids they reference. If
|  a pgid/sid is zero, i.e. from an ancestor pid-ns, then the tag will
|  be zero.
| 
| 6) In container checkpoint, pids out of our namesapce are disallwed.
|  We don't do leak detection on pids objects (should we ?).
| 
| RESTART:
| 
| 1) We first call prepare_descendants() to set the ->checkpoint_ctx
|  of the restarting tasks, and _then_ read the pids data followed by
|  the tasks' pids data. We validate both against existing tasks.
| 
| 2) restore_read_pids() reads the pids data, validates that each pid
|  exists (*) and adds the pids to the objhash. Verify that the owner
|  task is within our restart context.
| 
| (*) We validate them from the root task's point of view, by seeing
|  that the task has the correct 'struct pid' pointer. NOTE: user-cr
|  does not support restart --no-pids when there are nested pis-ns,
|  because is it quite complicated to find ou the pids of all tasks
|  at all nested levels from userspace.
| 
| 3) restore_read_tasks() reads the tasks' pids data, validates each
|  task and adds it to the ctx->tasks_arr. Verify that the task is
|  within our restart context.
| 
| 4) We track the array of restarting _tasks_ and the active _task_
|  instead an array of restarting pids and the active pid. The helpers
|  to wake-up, sync, check active task etc were modified accordingly.
|  It improves and simplifies the logic, e.g. restore_activate_next().
| 
| 5) There are two special values for pgid/sid tags:
|  0 - means that it is from an ancestor namespace, so we verify that
|    this is the case. For sid, user-cr should have created the task
|    properly; for pgid, use the coordinator's (or coordinator's parent)
|    pid if from differnet namespace, or fail.
|  CKPT_PID_ROOT - means that we want to reuse the root task's sid,
|    useful for when the root task is _not_ a conatiner init (e.g. in
|    subtree c/r) and its session (like our pgrp) was inherited from
|    somewhere above).
| 
| 6) Restoring of a task's pgid was moved to when task is validated,
|  as this should be part of the validation.
| 
| NOTE: the patch does not yet allow non-linear nesting of pid-ns.
| This would require to make pid-ns a shared object and track it by
| the 'struct ckpt_pids' on the kernel side, and in userspace we'll
| need to update the logic of MakeForest algorithm to be pid-ns aware
| (probably similarly to how sid constraints are handled).
| 
| Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
| ---
|  include/linux/checkpoint_hdr.h   |   22 ++-
|  include/linux/checkpoint_types.h |   10 +-
|  kernel/checkpoint/checkpoint.c   |  440 +++++++++++++++++++++----------
|  kernel/checkpoint/process.c      |  108 +-------
|  kernel/checkpoint/restart.c      |  551 ++++++++++++++++++++++++++++++--------
|  kernel/checkpoint/sys.c          |    5 -
|  6 files changed, 773 insertions(+), 363 deletions(-)
| 
| diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
| index 922eff0..c0a548a 100644
| --- a/include/linux/checkpoint_hdr.h
| +++ b/include/linux/checkpoint_hdr.h
| @@ -107,7 +107,9 @@ enum {
|  	CKPT_HDR_SECURITY,
|  #define CKPT_HDR_SECURITY CKPT_HDR_SECURITY
| 
| -	CKPT_HDR_TREE = 101,
| +	CKPT_HDR_PIDS = 101,
| +#define CKPT_HDR_PIDS CKPT_HDR_PIDS
| +	CKPT_HDR_TREE,
|  #define CKPT_HDR_TREE CKPT_HDR_TREE
|  	CKPT_HDR_TASK,
|  #define CKPT_HDR_TASK CKPT_HDR_TASK
| @@ -358,20 +360,32 @@ struct ckpt_hdr_container {
|  	 */
|  } __attribute__((aligned(8)));;
| 
| +/* pids array */
| +struct ckpt_hdr_pids {
| +	struct ckpt_hdr h;
| +	__u32 nr_pids;
| +	__u32 nr_vpids;
| +} __attribute__((aligned(8)));

For consistency can we call this ckpt_hdr_pids_tree ?

| +
| +struct ckpt_pids {
| +	__u32 depth;
| +	__s32 numbers[1];
| +} __attribute__((aligned(8)));
| +

This actually corresponds to _one_ 'struct pid' right ? Can we rename to
'struct ckpt_pid' or ckpt_struct_pid ?

|  /* task tree */
|  struct ckpt_hdr_tree {
|  	struct ckpt_hdr h;
| -	__s32 nr_tasks;
| +	__u32 nr_tasks;
|  } __attribute__((aligned(8)));

And this to, ckpt_hdr_task_tree ?

| 
| -struct ckpt_pids {
| +struct ckpt_task_pids {
|  	/* These pids are in the root_nsproxy's pid ns */
|  	__s32 vpid;
|  	__s32 vppid;
|  	__s32 vtgid;
|  	__s32 vpgid;
|  	__s32 vsid;
| -	__s32 depth; /* pid namespace depth relative to container init */
| +	__u32 depth;
|  } __attribute__((aligned(8)));
| 
|  /* pids */
| diff --git a/include/linux/checkpoint_types.h b/include/linux/checkpoint_types.h
| index 87a569a..60c664f 100644
| --- a/include/linux/checkpoint_types.h
| +++ b/include/linux/checkpoint_types.h
| @@ -68,16 +68,14 @@ struct ckpt_ctx {
| 
|  	int nr_vpids;			/* total count of vpids */
| 
| -	/* [checkpoint] */
| -	struct task_struct *tsk;	/* current target task */
|  	struct task_struct **tasks_arr;	/* array of all tasks */
|  	int nr_tasks;			/* size of tasks array */
| 
| +	/* [checkpoint] */
| +	struct task_struct *tsk;	/* current target task */
| +
|  	/* [restart] */
| -	struct pid_namespace *coord_pidns;/* coordinator pid_ns */
| -	struct ckpt_pids *pids_arr;	/* array of all pids [restart] */
| -	int nr_pids;			/* size of pids array */
| -	int active_pid;			/* (next) position in pids array */
| +	int active_task;		/* (next) position in pids array */
|  	atomic_t nr_total;		/* total tasks count */
|  	struct completion complete;	/* completion for container root */
|  	wait_queue_head_t waitq;	/* waitqueue for restarting tasks */
| diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
| index 42de30a..f351f49 100644
| --- a/kernel/checkpoint/checkpoint.c
| +++ b/kernel/checkpoint/checkpoint.c
| @@ -313,133 +313,6 @@ static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
|  	return ret;
|  }
| 
| -#define CKPT_HDR_PIDS_CHUNK	256
| -
| -/*
| - * Write the pids in ctx->root_nsproxy->pidns.  This info is
| - * needed at restart to unambiguously dereference tasks.
| - */
| -static int checkpoint_pids(struct ckpt_ctx *ctx)
| -{
| -	struct ckpt_pids *h;
| -	struct pid_namespace *root_pidns;
| -	struct task_struct *task;
| -	struct task_struct **tasks_arr;
| -	int nr_tasks, n, pos = 0, ret = 0;
| -
| -	root_pidns = ctx->root_nsproxy->pid_ns;
| -	tasks_arr = ctx->tasks_arr;
| -	nr_tasks = ctx->nr_tasks;
| -	BUG_ON(nr_tasks <= 0);
| -
| -	ret = ckpt_write_obj_type(ctx, NULL,
| -				  sizeof(*h) * nr_tasks,
| -				  CKPT_HDR_BUFFER);
| -	if (ret < 0)
| -		return ret;
| -
| -	h = ckpt_hdr_get(ctx, sizeof(*h) * CKPT_HDR_PIDS_CHUNK);
| -	if (!h)
| -		return -ENOMEM;
| -
| -	do {
| -		rcu_read_lock();
| -		for (n = 0; n < min(nr_tasks, CKPT_HDR_PIDS_CHUNK); n++) {
| -			struct pid_namespace *task_pidns;
| -			task = tasks_arr[pos];
| -
| -			h[n].vpid = task_pid_nr_ns(task, root_pidns);
| -			h[n].vtgid = task_tgid_nr_ns(task, root_pidns);
| -			h[n].vpgid = task_pgrp_nr_ns(task, root_pidns);
| -			h[n].vsid = task_session_nr_ns(task, root_pidns);
| -			h[n].vppid = task_tgid_nr_ns(task->real_parent,
| -					root_pidns);
| -			task_pidns = task_active_pid_ns(task);
| -			h[n].depth = task_pidns->level - root_pidns->level;
| -
| -			ckpt_debug("task[%d]: vpid %d vtgid %d parent %d\n",
| -				   pos, h[n].vpid, h[n].vtgid, h[n].vppid);
| -			ctx->nr_vpids += h[n].depth;
| -			pos++;
| -		}
| -		rcu_read_unlock();
| -
| -		n = min(nr_tasks, CKPT_HDR_PIDS_CHUNK);
| -		ret = ckpt_kwrite(ctx, h, n * sizeof(*h));
| -		if (ret < 0)
| -			break;
| -
| -		nr_tasks -= n;
| -	} while (nr_tasks > 0);
| -
| -	_ckpt_hdr_put(ctx, h, sizeof(*h) * CKPT_HDR_PIDS_CHUNK);
| -	return ret;
| -}
| -
| -static int checkpoint_vpids(struct ckpt_ctx *ctx)
| -{
| -	__s32 *h;  /* vpid array */
| -	struct pid_namespace *root_pidns, *task_pidns = NULL, *active_pidns;
| -	struct task_struct *task;
| -	int ret, nr_tasks = ctx->nr_tasks;
| -	int tidx = 0; /* index into task array */
| -	int hidx = 0; /* pids written into current __s32 chunk */
| -	int vidx = 0; /* vpid index for current task */
| -
| -	root_pidns = ctx->root_nsproxy->pid_ns;
| -	nr_tasks = ctx->nr_tasks;
| -
| -	ret = ckpt_write_obj_type(ctx, NULL,
| -				  sizeof(*h) * ctx->nr_vpids,
| -				  CKPT_HDR_BUFFER);
| -	if (ret < 0)
| -		return ret;
| -
| -	h = ckpt_hdr_get(ctx, sizeof(*h) * CKPT_HDR_PIDS_CHUNK);
| -	if (!h)
| -		return -ENOMEM;
| -
| -	do {
| -		rcu_read_lock();
| -		while (tidx < nr_tasks && hidx < CKPT_HDR_PIDS_CHUNK) {
| -			int nsdelta;
| -
| -			task = ctx->tasks_arr[tidx];
| -			active_pidns = task_active_pid_ns(task);
| -			nsdelta = active_pidns->level - root_pidns->level;
| -			if (hidx + nsdelta - vidx > CKPT_HDR_PIDS_CHUNK)
| -				/*
| -				 * We will release rcu before recording the
| -				 * remaining vpids, but neither task nor its
| -				 * pid can disappear.
| -				 */
| -				nsdelta = CKPT_HDR_PIDS_CHUNK - hidx + vidx;
| -
| -			if (vidx == 0)
| -				task_pidns = active_pidns;
| -			while (vidx++ < nsdelta) {
| -				h[hidx++] = task_pid_nr_ns(task, task_pidns);
| -				task_pidns = task_pidns->parent;
| -			}
| -
| -			if (task_pidns == root_pidns) {
| -				tidx++;
| -				vidx = 0;
| -			}
| -		}
| -		rcu_read_unlock();
| -
| -		ret = ckpt_kwrite(ctx, h, hidx * sizeof(*h));
| -		if (ret < 0)
| -			break;
| -
| -		hidx = 0;
| -	} while (tidx < nr_tasks);
| -
| -	_ckpt_hdr_put(ctx, h, sizeof(*h) * CKPT_HDR_PIDS_CHUNK);
| -	return ret;
| -}
| -
|  static int collect_objects(struct ckpt_ctx *ctx)
|  {
|  	int n, ret = 0;
| @@ -546,31 +419,321 @@ static int build_tree(struct ckpt_ctx *ctx)
|  	return 0;
|  }
| 
| +static int checkpoint_pids_build(struct ckpt_ctx *ctx,
| +				 struct flex_array *pids_arr,
| +				 int *nr_pids, int *nr_vpids)
| +{
| +	struct pid_namespace *root_pidns;
| +	struct pid *pid, *tgid, *pgrp, *session;
| +	struct pid *root_session;
| +	struct task_struct *task;
| +	int i = 0, depth = 0;
| +	int n, new, ret = 0;
| +
| +	/* safe because we reference the task */
| +	root_session = get_pid(task_session(ctx->root_task));
| +	root_pidns = ctx->root_nsproxy->pid_ns;
| +
| +	for (n = 0; n < ctx->nr_tasks; n++) {
| +		task = ctx->tasks_arr[n];
| +
| +		rcu_read_lock();
| +		pid = get_pid(task_pid(task));
| +		tgid = get_pid(task_tgid(task));
| +		pgrp = get_pid(task_pgrp(task));
| +		session = get_pid(task_session(task));
| +		rcu_read_unlock();
| +
| +		/*
| +		 * How to handle references to pids outside our pid-ns ?
| +		 * In container checkpoint, such pids are prohibited, so
| +		 * we report an error.
| +		 * In subtree checkpoint it is valid, however, we don't
| +		 * collect them here to not leak data (it is irrelevant
| +		 * to userspace anyway), Instead, in checkpoint_tree() we
| +		 * substitute 0 for the such pgrp/session entries.
| +		 */
| +
| +		/* pid */
| +		ret = ckpt_obj_lookup_add(ctx, pid,
| +					  CKPT_OBJ_PID, &new);
| +		if (ret >= 0 && new) {
| +			depth += pid->level - root_pidns->level;

'depth' here was a bit confusing to me. We are really counting of the
number of vpids. So, can you rename 'depth' to nr_pids ?

(i.e if you find a process with pid and tgid two levels deep, it initially
appeared that the depth would be 4. But the depth is still 2 and the number
of vpids is 4 right ?)
| +			ret = flex_array_put(pids_arr, i++, pid, GFP_KERNEL);
| +			new = 0;
| +		}
| +
| +		/* tgid: if tgid != pid) */
| +		if (ret >= 0 && tgid != pid)
| +			ret = ckpt_obj_lookup_add(ctx, tgid,
| +						  CKPT_OBJ_PID, &new);
| +		if (ret >= 0 && new) {
| +			depth += tgid->level - root_pidns->level;
| +			ret = flex_array_put(pids_arr, i++, tgid, GFP_KERNEL);
| +			new = 0;
| +		}
| +
| +		/*
| +		 * pgrp: if in our pid-namespace, and
| +		 *       if pgrp != tgid, and if pgrp != root_session
| +		 */
| +		if (pid_nr_ns(pgrp, root_pidns) == 0) {
| +			/* pgrp must be ours in container checkpoint */
| +			if (!(ctx->uflags & CHECKPOINT_SUBTREE))
| +				ret = -EBUSY;
| +		} else if (ret >= 0 && pgrp != tgid && pgrp != root_session)
| +			ret = ckpt_obj_lookup_add(ctx, pgrp,
| +						  CKPT_OBJ_PID, &new);
| +		if (ret >= 0 && new) {
| +			depth += pgrp->level - root_pidns->level;
| +			ret = flex_array_put(pids_arr, i++, pgrp, GFP_KERNEL);
| +			new = 0;
| +		}
| +
| +		/*
| +		 * session: if in our pid-namespace, and
| +		 *          if session != tgid, and if session != root_session
| +		 */
| +		if (pid_nr_ns(session, root_pidns) == 0) {
| +			/* session must be ours in container checkpoint */
| +			if (!(ctx->uflags & CHECKPOINT_SUBTREE))
| +				ret = -EBUSY;
| +		} else if (ret >= 0 && session != tgid && session != root_session)
| +			ret = ckpt_obj_lookup_add(ctx, session,
| +						  CKPT_OBJ_PID, &new);
| +		if (ret >= 0 && new) {
| +			depth += session->level - root_pidns->level;
| +			ret = flex_array_put(pids_arr, i++, session, GFP_KERNEL);
| +		}
| +
| +		put_pid(pid);
| +		put_pid(tgid);
| +		put_pid(pgrp);
| +		put_pid(session);

We save the pid pointers in the flex_array right ? If we put the references
here, the pointers in flex_array don't have a reference, so the pid pointer
access in checkpoint_pids_dump() is unsafe ?

Or is it that the process tree is frozen so the pid won't go away ? If
so do we need the get_pid() and put_pid() in this function ?

| +
| +		if (ret < 0)
| +			break;
| +	}
| +
| +	*nr_pids = i;
| +	*nr_vpids = depth;
| +
| +	ckpt_debug("nr_pids = %d, nr_vpids = %d\n", i, depth);
| +	return ret;
| +}
| +
| +static int checkpoint_pids_dump(struct ckpt_ctx *ctx,
| +				struct flex_array *pids_arr,
| +				int nr_pids, int nr_vpids)
| +{
| +	struct ckpt_hdr_pids *hh;
| +	struct ckpt_pids *h;
| +	struct pid *pid;
| +	char *buf;
| +	int root_level;
| +	int len, pos;
| +	int depth = 0;

Here too, using 'depth' to count nr_vpids is a bit confusing :-)

| +	int i, n = 0;
| +	int ret;
| +
| +	hh = ckpt_hdr_get_type(ctx, sizeof(*hh), CKPT_HDR_PIDS);
| +	if (!hh)
| +		return -ENOMEM;
| +
| +	hh->nr_pids = nr_pids;
| +	hh->nr_vpids = nr_vpids;
| +
| +	ret = ckpt_write_obj(ctx, &hh->h);
| +	ckpt_hdr_put(ctx, hh);
| +	if (ret < 0)
| +		return ret;
| +
| +	pos = (nr_pids * sizeof(*h)) + (nr_vpids * sizeof(__s32));
| +	ret = ckpt_write_obj_type(ctx, NULL, pos, CKPT_HDR_BUFFER);
| +	if (ret < 0)
| +		return ret;
| +
| +	buf = ckpt_hdr_get(ctx, PAGE_SIZE);
| +	if (!buf)
| +		return -ENOMEM;
| +
| +	root_level = ctx->root_nsproxy->pid_ns->level;
| +
| +	while (n < nr_pids) {
| +		pos = 0;
| +
| +		rcu_read_lock();
| +		while (1) {
| +			pid = flex_array_get(pids_arr, n);
| +			len = sizeof(*h) + pid->level * sizeof(__s32);

Hmm. pid->level is the global level here right ? So if we checkpoint a
container 2 levels deep, we don't need to save the vpids for levels 0,1.
do we ?   Or should we s/pid->level/(pid->level - root->level)/ (like
we do for h->depth below ?

| +
| +			/* need to flush current buffer ? */
| +			if (pos + len > PAGE_SIZE || n == nr_pids)
| +				break;
| +
| +			h = (struct ckpt_pids *) &buf[pos];
| +			h->depth = pid->level - root_level;
| +			for (i = 0; i <= h->depth; i++)
| +				h->numbers[i] = pid->numbers[pid->level + i].nr;
| +			depth += h->depth;
| +			pos += len;
| +			n++;
| +		}
| +		rcu_read_unlock();
| +
| +		/* something must have changed since last count... */
| +		if (depth > nr_vpids) {
| +			ret = -EBUSY;
| +			break;
| +		}
| +
| +		ret = ckpt_kwrite(ctx, buf, pos);
| +		if (ret < 0)
| +			break;

Do we need to memset(buf, 0, sizeof(buf)) here ? Specially if we expect
to fill 0s in ancestor pid namespaces (in the above example of
checkpointing a container 2 levels deep, do we want to write zeros for
the pid in levels 0,1) ?

Suka

Re: [PATCH 4/5] c/r: checkpoint and restart pids objects

[Oren Laadan]

Suka,

Thanks for the review.

On 02/05/2011 04:43 PM, Sukadev Bhattiprolu wrote:
> Oren:
> 
> I am still reviewing this patchset, but have a few questions/comments
> below on this patch.
> 
> | From: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
> | Subject: [PATCH 4/5] c/r: checkpoint and restart pids objects
> | 
> | Make use of (shared) pids objects instead of simply saving the pid_t
> | numbers in both checkpoint and restart.
> | 
> | The motivation for this change is twofold. First, since pid-ns came to
> | life pid's in the kenrel _are_ shared objects and should be treated as
> | such. This is useful e.g. for tty handling and also file-ownership
> | (the latter waiting for this feature). Second, to properly support
> | nested namesapces we need to report with each pid the entire list of
> | pid numbers, not only a single pid. While current we do that for all
> | "live" pids (those that belong to live tasks), we didn't do it for
> | "dead" pids (to be assigned to ghost restarting tasks).
> | 
> | Note, that ideally the list of vpids of a pid object should also
> | include the pid-ns to which each level belongs; however, in this patch
> | we don't yet hanlde that. So only linear pid-nesting works well and
> | not arbitrary tree.
> | 
> | DICLAIMER: this patch is big and intrusive!  Here is a summary of the
> | changes that it makes:

[...]

> | diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
> | index 922eff0..c0a548a 100644
> | --- a/include/linux/checkpoint_hdr.h
> | +++ b/include/linux/checkpoint_hdr.h
> | @@ -107,7 +107,9 @@ enum {
> |  	CKPT_HDR_SECURITY,
> |  #define CKPT_HDR_SECURITY CKPT_HDR_SECURITY
> | 
> | -	CKPT_HDR_TREE = 101,
> | +	CKPT_HDR_PIDS = 101,
> | +#define CKPT_HDR_PIDS CKPT_HDR_PIDS
> | +	CKPT_HDR_TREE,
> |  #define CKPT_HDR_TREE CKPT_HDR_TREE
> |  	CKPT_HDR_TASK,
> |  #define CKPT_HDR_TASK CKPT_HDR_TASK
> | @@ -358,20 +360,32 @@ struct ckpt_hdr_container {
> |  	 */
> |  } __attribute__((aligned(8)));;
> | 
> | +/* pids array */
> | +struct ckpt_hdr_pids {
> | +	struct ckpt_hdr h;
> | +	__u32 nr_pids;
> | +	__u32 nr_vpids;
> | +} __attribute__((aligned(8)));
> 
> For consistency can we call this ckpt_hdr_pids_tree ?

'struct ckpt_hdr_pids' and  'struct ckpt_pids' are related, and
do not provide information about the process tree. See also,
for example, 'struct ckpt_eventpoll_item' and the .._hdr_.. one.

> 
> | +
> | +struct ckpt_pids {
> | +	__u32 depth;
> | +	__s32 numbers[1];
> | +} __attribute__((aligned(8)));
> | +
> 
> This actually corresponds to _one_ 'struct pid' right ? Can we rename to
> 'struct ckpt_pid' or ckpt_struct_pid ?

Yes, it corresponds to a single pid object, which has _multiple_
(rather than a single) pids numbers --> hence the name.

> 
> |  /* task tree */
> |  struct ckpt_hdr_tree {
> |  	struct ckpt_hdr h;
> | -	__s32 nr_tasks;
> | +	__u32 nr_tasks;
> |  } __attribute__((aligned(8)));
> 
> And this to, ckpt_hdr_task_tree ?

Ok.

[...]

> | +	for (n = 0; n < ctx->nr_tasks; n++) {
> | +		task = ctx->tasks_arr[n];
> | +
> | +		rcu_read_lock();
> | +		pid = get_pid(task_pid(task));
> | +		tgid = get_pid(task_tgid(task));
> | +		pgrp = get_pid(task_pgrp(task));
> | +		session = get_pid(task_session(task));
> | +		rcu_read_unlock();
> | +
> | +		/*
> | +		 * How to handle references to pids outside our pid-ns ?
> | +		 * In container checkpoint, such pids are prohibited, so
> | +		 * we report an error.
> | +		 * In subtree checkpoint it is valid, however, we don't
> | +		 * collect them here to not leak data (it is irrelevant
> | +		 * to userspace anyway), Instead, in checkpoint_tree() we
> | +		 * substitute 0 for the such pgrp/session entries.
> | +		 */
> | +
> | +		/* pid */
> | +		ret = ckpt_obj_lookup_add(ctx, pid,
> | +					  CKPT_OBJ_PID, &new);
> | +		if (ret >= 0 && new) {
> | +			depth += pid->level - root_pidns->level;
> 
> 'depth' here was a bit confusing to me. We are really counting of the
> number of vpids. So, can you rename 'depth' to nr_pids ?

So either 'vpids', or 'levels'. The problem with 'nr_pids' is that
it's ambiguous: could be number of pid-objects, or pid-numbers.

> 
> (i.e if you find a process with pid and tgid two levels deep, it initially
> appeared that the depth would be 4. But the depth is still 2 and the number
> of vpids is 4 right ?)

Yes, it is summing the depths.

> | +			ret = flex_array_put(pids_arr, i++, pid, GFP_KERNEL);
> | +			new = 0;
> | +		}
> | +
> | +		/* tgid: if tgid != pid) */
> | +		if (ret >= 0 && tgid != pid)
> | +			ret = ckpt_obj_lookup_add(ctx, tgid,
> | +						  CKPT_OBJ_PID, &new);
> | +		if (ret >= 0 && new) {
> | +			depth += tgid->level - root_pidns->level;
> | +			ret = flex_array_put(pids_arr, i++, tgid, GFP_KERNEL);
> | +			new = 0;
> | +		}
> | +
> | +		/*
> | +		 * pgrp: if in our pid-namespace, and
> | +		 *       if pgrp != tgid, and if pgrp != root_session
> | +		 */
> | +		if (pid_nr_ns(pgrp, root_pidns) == 0) {
> | +			/* pgrp must be ours in container checkpoint */
> | +			if (!(ctx->uflags & CHECKPOINT_SUBTREE))
> | +				ret = -EBUSY;
> | +		} else if (ret >= 0 && pgrp != tgid && pgrp != root_session)
> | +			ret = ckpt_obj_lookup_add(ctx, pgrp,
> | +						  CKPT_OBJ_PID, &new);
> | +		if (ret >= 0 && new) {
> | +			depth += pgrp->level - root_pidns->level;
> | +			ret = flex_array_put(pids_arr, i++, pgrp, GFP_KERNEL);
> | +			new = 0;
> | +		}
> | +
> | +		/*
> | +		 * session: if in our pid-namespace, and
> | +		 *          if session != tgid, and if session != root_session
> | +		 */
> | +		if (pid_nr_ns(session, root_pidns) == 0) {
> | +			/* session must be ours in container checkpoint */
> | +			if (!(ctx->uflags & CHECKPOINT_SUBTREE))
> | +				ret = -EBUSY;
> | +		} else if (ret >= 0 && session != tgid && session != root_session)
> | +			ret = ckpt_obj_lookup_add(ctx, session,
> | +						  CKPT_OBJ_PID, &new);
> | +		if (ret >= 0 && new) {
> | +			depth += session->level - root_pidns->level;
> | +			ret = flex_array_put(pids_arr, i++, session, GFP_KERNEL);
> | +		}
> | +
> | +		put_pid(pid);
> | +		put_pid(tgid);
> | +		put_pid(pgrp);
> | +		put_pid(session);
> 
> We save the pid pointers in the flex_array right ? If we put the references
> here, the pointers in flex_array don't have a reference, so the pid pointer
> access in checkpoint_pids_dump() is unsafe ?
> 
> Or is it that the process tree is frozen so the pid won't go away ? If
> so do we need the get_pid() and put_pid() in this function ?

We get a reference inside the rcu_read_lock() so that we could safely
access them after we drop the lock. Then we add each (new) pid to the
objhash - which will take another reference to it. Finally we drop 
the local reference no longer needed.

I'll a comment to make it clear.

> | +
> | +		if (ret < 0)
> | +			break;
> | +	}
> | +
> | +	*nr_pids = i;
> | +	*nr_vpids = depth;
> | +
> | +	ckpt_debug("nr_pids = %d, nr_vpids = %d\n", i, depth);
> | +	return ret;
> | +}
> | +
> | +static int checkpoint_pids_dump(struct ckpt_ctx *ctx,
> | +				struct flex_array *pids_arr,
> | +				int nr_pids, int nr_vpids)
> | +{
> | +	struct ckpt_hdr_pids *hh;
> | +	struct ckpt_pids *h;
> | +	struct pid *pid;
> | +	char *buf;
> | +	int root_level;
> | +	int len, pos;
> | +	int depth = 0;
> 
> Here too, using 'depth' to count nr_vpids is a bit confusing :-)

Ok - will change as above.

> 
> | +	int i, n = 0;
> | +	int ret;
> | +
> | +	hh = ckpt_hdr_get_type(ctx, sizeof(*hh), CKPT_HDR_PIDS);
> | +	if (!hh)
> | +		return -ENOMEM;
> | +
> | +	hh->nr_pids = nr_pids;
> | +	hh->nr_vpids = nr_vpids;
> | +
> | +	ret = ckpt_write_obj(ctx, &hh->h);
> | +	ckpt_hdr_put(ctx, hh);
> | +	if (ret < 0)
> | +		return ret;
> | +
> | +	pos = (nr_pids * sizeof(*h)) + (nr_vpids * sizeof(__s32));
> | +	ret = ckpt_write_obj_type(ctx, NULL, pos, CKPT_HDR_BUFFER);
> | +	if (ret < 0)
> | +		return ret;
> | +
> | +	buf = ckpt_hdr_get(ctx, PAGE_SIZE);
> | +	if (!buf)
> | +		return -ENOMEM;
> | +
> | +	root_level = ctx->root_nsproxy->pid_ns->level;
> | +
> | +	while (n < nr_pids) {
> | +		pos = 0;
> | +
> | +		rcu_read_lock();
> | +		while (1) {
> | +			pid = flex_array_get(pids_arr, n);
> | +			len = sizeof(*h) + pid->level * sizeof(__s32);
> 
> Hmm. pid->level is the global level here right ? So if we checkpoint a
> container 2 levels deep, we don't need to save the vpids for levels 0,1.
> do we ?   Or should we s/pid->level/(pid->level - root->level)/ (like
> we do for h->depth below ?

The latter. Good catch !

> 
> | +
> | +			/* need to flush current buffer ? */
> | +			if (pos + len > PAGE_SIZE || n == nr_pids)
> | +				break;
> | +
> | +			h = (struct ckpt_pids *) &buf[pos];
> | +			h->depth = pid->level - root_level;
> | +			for (i = 0; i <= h->depth; i++)
> | +				h->numbers[i] = pid->numbers[pid->level + i].nr;
> | +			depth += h->depth;
> | +			pos += len;
> | +			n++;
> | +		}
> | +		rcu_read_unlock();
> | +
> | +		/* something must have changed since last count... */
> | +		if (depth > nr_vpids) {
> | +			ret = -EBUSY;
> | +			break;
> | +		}
> | +
> | +		ret = ckpt_kwrite(ctx, buf, pos);
> | +		if (ret < 0)
> | +			break;
> 
> Do we need to memset(buf, 0, sizeof(buf)) here ? Specially if we expect
> to fill 0s in ancestor pid namespaces (in the above example of
> checkpointing a container 2 levels deep, do we want to write zeros for
> the pid in levels 0,1) ?

We shouldn't need it - assuming we fix the above as noted.

Thanks,

Oren.

[PATCH 5/5] c/r: use pids objects for the pgrp/old_pgdp of ttys

[Oren Laadan]

Make tty_old_pgrp and tty_pgrp use the shared pid instead of saving
the actual pid number in {checkpoint,restore}_signal().

Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 kernel/signal.c |   42 ++++++++++++++++++++++++++++++++----------
 1 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 3842f5d..5c174a9 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3218,25 +3218,34 @@ static int checkpoint_signal(struct ckpt_ctx *ctx, struct task_struct *t)
 
 	/* tty */
 	if (signal->leader) {
-		h->tty_old_pgrp = ckpt_pid_nr(ctx, signal->tty_old_pgrp);
+		h->tty_old_pgrp = ckpt_lookup_pid(ctx, signal->tty_old_pgrp);
 		tty = tty_kref_get(signal->tty);
 		if (tty) {
 			/* irq is already disabled */
 			spin_lock(&tty->ctrl_lock);
-			h->tty_pgrp = ckpt_pid_nr(ctx, tty->pgrp);
+			h->tty_pgrp = ckpt_lookup_pid(ctx, tty->pgrp);
 			spin_unlock(&tty->ctrl_lock);
-			tty_kref_put(tty);
 		}
 	}
 
 	unlock_task_sighand(t, &flags);
 
 	/*
+	 * tty_pgrp must be in our namespace, since we are the
+	 * session leader and could not have unshared pidns !
+	 */
+	if (tty && h->tty_pgrp == 0) {
+		ckpt_err(ctx, -EBUSY, "%(T)tty_pgrp outside namespace\n");
+		ret = -EBUSY;
+		goto out;
+	}
+
+	/*
 	 * If the session is in an ancestor namespace, skip this tty
 	 * and set tty_objref = 0. It will not be explicitly restored,
 	 * but rather inherited from parent pid-ns at restart time.
 	 */
-	if (tty && ckpt_pid_nr(ctx, tty->session) > 0) {
+	if (tty && ckpt_lookup_pid(ctx, tty->session) > 0) {
 		h->tty_objref = checkpoint_obj(ctx, tty, CKPT_OBJ_TTY);
 		if (h->tty_objref < 0)
 			ret = h->tty_objref;
@@ -3255,6 +3264,7 @@ static int checkpoint_signal(struct ckpt_ctx *ctx, struct task_struct *t)
 	list_splice(&shared_pending.list, &signal->shared_pending.list);
 	unlock_task_sighand(t, &flags);
  out:
+	tty_kref_put(tty);
 	ckpt_hdr_put(ctx, h);
 	return ret;
 }
@@ -3339,6 +3349,10 @@ static int restore_signal(struct ckpt_ctx *ctx)
 
 	/* tty - session */
 	if (h->tty_objref) {
+		/*
+		 * should only get here if we are session leader, but
+		 * we don't explicitly check: forced by calls below
+		 */
 		tty = ckpt_obj_fetch(ctx, h->tty_objref, CKPT_OBJ_TTY);
 		if (IS_ERR(tty)) {
 			ret = PTR_ERR(tty);
@@ -3354,6 +3368,11 @@ static int restore_signal(struct ckpt_ctx *ctx)
 			 * If tty_pgrp == CKPT_PID_NULL, below will
 			 * fail, so no need for explicit test
 			 */
+			pgrp = ckpt_obj_fetch(ctx, h->tty_pgrp, CKPT_OBJ_PID);
+			if (IS_ERR(pgrp)) {
+				ret = PTR_ERR(pgrp);
+				goto out;
+			}
 			ret = do_tiocspgrp(tty, tty_pair_get_tty(tty),
 					   pid_vnr(pgrp));
 			if (ret < 0)
@@ -3382,13 +3401,16 @@ static int restore_signal(struct ckpt_ctx *ctx)
 	do_setitimer(ITIMER_VIRTUAL, &itimer, NULL);
 	do_setitimer(ITIMER_PROF, &itimer, NULL);
 
-	/* tty - tty_old_pgrp */
-	if (current->signal->leader && h->tty_old_pgrp != CKPT_PID_NULL) {
-		rcu_read_lock();
-		pgrp = get_pid(_ckpt_find_pgrp(ctx, h->tty_old_pgrp));
-		rcu_read_unlock();
-		if (!pgrp)
+	/*
+	 * tty - tty_old_pgrp: only for session leaders and for valid
+	 * tty_old_pgrp, ie, within our namespace, and not CKPT_PID_NULL.
+	 */
+	if (current->signal->leader && h->tty_old_pgrp > 0) {
+		pgrp = ckpt_obj_fetch(ctx, h->tty_old_pgrp, CKPT_OBJ_PID);
+		if (IS_ERR(pgrp)) {
+			ret = PTR_ERR(pgrp);
 			goto out;
+		}
 	}
 
 	spin_lock_irq(&current->sighand->siglock);
-- 
1.7.1